QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETINGS

The following are answers to certain questions that you may have regarding the special meetings. The parties urge you to read carefully the remainder of this document because the information in this section may not provide all the information that might be important to you in determining how to vote. Additional important information is also contained in the appendices to, and the documents incorporated by reference into, this document. In this joint proxy statement/prospectus, we refer to Atlantic Capital Bancshares, Inc. as “Atlantic Capital,” First Security Group, Inc. as “First Security,” Atlantic Capital Bank, a wholly owned subsidiary of Atlantic Capital, as “Atlantic Capital Bank,” FSGBank, National Association, a wholly owned subsidiary of First Security, as “FSGBank,” and FSGBank after it changes its name to “Atlantic Capital Bank, National Association” following the bank merger, as “Surviving Bank.”

A: Atlantic Capital and First Security have entered into an Agreement and Plan of Merger, dated as of March 25, 2015 (as amended on June 8, 2015, the “merger agreement”) pursuant to which First Security will merge with and into Atlantic Capital, with Atlantic Capital continuing as the surviving company (the “merger”). Immediately following the merger, FSGBank, a wholly owned bank subsidiary of First Security, will merge with and into Atlantic Capital’s wholly owned bank subsidiary, Atlantic Capital Bank, with FSGBank continuing as the surviving bank (the “bank merger”). A copy of the merger agreement is included in this joint proxy statement/prospectus as Appendix A.

The merger cannot be completed unless, among other things:

In addition, both Atlantic Capital and First Security are soliciting proxies from their shareholders with respect to proposals to adjourn the Atlantic Capital and First Security special meetings, as applicable, and if necessary or appropriate, including to solicit additional proxies in favor of their respective proposals to approve the merger agreement and the transactions contemplated thereby, if there are insufficient votes at the time of such adjournment to approve such proposals. First Security shareholders also will be asked to approve the merger-related compensation proposal.

Each of Atlantic Capital and First Security will hold separate special meetings to obtain these approvals. This joint proxy statement/prospectus contains important information about the merger and the other proposals being voted on at the special meetings, and you should read it carefully. It is a joint proxy statement because both the Atlantic Capital and First Security boards of directors are soliciting proxies from their respective shareholders. It is a prospectus because Atlantic Capital will issue shares of Atlantic Capital common stock to holders of First Security common stock in connection with the merger. The enclosed materials allow you to have your shares voted by proxy without attending your respective meeting. Your vote is important. We encourage you to submit your proxy as soon as possible.

A: We believe the combination of Atlantic Capital and First Security will provide Atlantic Capital with significant opportunities for enhanced revenue and growth. Each of the Atlantic Capital and First Security boards of directors has determined that the merger is fair to, and in the best interest of, its respective shareholders, and

recommends that its shareholders vote for their respective proposals. You should review the reasons for the merger described in greater detail under “The Merger—First Security’s Reasons for the Merger and Recommendation of the First Security Board of Directors” and “The Merger—Atlantic Capital’s Reasons for the Merger and Recommendation of the Atlantic Capital Board of Directors.”

A: Atlantic Capital shareholders: If the merger is completed, Atlantic Capital shareholders will not receive any merger consideration and will continue to hold their shares of Atlantic Capital common stock. Upon the completion of the merger, we expect that Atlantic Capital common stock will be listed on The Nasdaq Global Select Market (“Nasdaq”) and will trade under the symbol “[●].”

First Security shareholders: If the merger is completed, First Security shareholders will receive, for each share of First Security common stock held, the right to receive the per share merger consideration provided for in the merger agreement (the “Merger Consideration”), which shall consist of: (i) cash in the amount of $2.35 per share, or (ii) 0.188 shares (the “Exchange Ratio”) of Atlantic Capital common stock.

First Security shareholders may elect to receive all cash, all stock, or any combination of cash and stock. Such elections will be due five business days prior to the effective time of the merger (the “Effective Time”). However, the amount of aggregate cash consideration will be a minimum of $47,097,708 and a maximum of $54,947,326, which will require between 30% to 35% shares of First Security common stock, or between 20,041,578 shares of First Security common stock (the “Cash Election Minimum Threshold”) and 23,381,841 shares of First Security common stock (the “Cash Election Maximum Threshold”) to receive cash.

If the Cash Election Minimum Threshold is undersubscribed, the Merger Consideration will be allocated as follows:

If the Cash Election Maximum Threshold is oversubscribed, the Merger Consideration will be allocated as follows:

If the number of cash election shares is equal to or greater than the Cash Election Minimum Threshold and equal to or lesser than the Cash Election Maximum Threshold, the Merger Consideration will be allocated as follows:

A: First Security shareholders are receiving an election form with this joint proxy statement/prospectus. You should complete the election form to specify your preferred type of Merger Consideration (or provide instructions to your broker if you hold your shares in “street name”). If you wish to make an election, you should complete the election form and send it in the envelope provided to Atlantic Capital’s exchange agent, Computershare. To make an effective election, your properly executed election form must be received by Computershare before the close of business five days prior to the Effective Time (the “Election Deadline”). Please read the instructions on the election form for information on completing the form. If you do not return a completed, properly executed election form by the Election Deadline, you will be treated as having made no election and will receive cash or stock or a combination thereof based on the elections made by other First Security shareholders. We will make a public announcement of the expected closing date of the merger at least ten days prior to the anticipated Effective Time.

A: Yes, you can change your election by submitting a new election form to Atlantic Capital’s exchange agent, Computershare, so that it is received prior to the Election Deadline. After the Election Deadline, you may not change your election.

A: The value of the stock consideration received in the merger will depend on the value of Atlantic Capital common stock for which there is currently no public market. On March 25, 2015, in connection with the merger agreement, Atlantic Capital entered into a securities purchase agreement which provides for the sale of approximately 1,984,127 shares of Atlantic Capital common stock at $12.60 per share, which, based on the 0.188 share merger exchange ratio, represents an implied value of $2.37 per share of First Security common stock. It is possible that the consideration received in exchange for each share of First Security common stock could be less than the market value of such share of First Security common stock prior to the merger.

A: The Atlantic Capital Board recommends that Atlantic Capital shareholders vote “FOR” the Atlantic Capital merger proposal and “FOR” the Atlantic Capital adjournment proposal.

A: The First Security Board recommends that First Security shareholders vote “FOR” the First Security merger proposal, “FOR” the merger-related compensation proposal, and “FOR” the First Security adjournment proposal.

A: Atlantic Capital special meeting. The Atlantic Capital special meeting will be held at [●], Atlanta, Georgia, on [●], 2015, at [●] local time.

First Security special meeting. The First Security special meeting will be held at [●], Chattanooga, Tennessee, on [●], 2015, at [●] local time.

A: Atlantic Capital special meeting. Holders of record of Atlantic Capital common stock at the close of business on [●], 2015, which is the date that the Atlantic Capital Board has fixed as the record date for the Atlantic Capital special meeting, are entitled to vote at the special meeting.

First Security special meeting. Holders of record of First Security common stock at the close of business on [●], 2015, which is the date that the First Security Board has fixed as the record date for the First Security special meeting, are entitled to vote at the special meeting.

A: After you have carefully read this joint proxy statement/prospectus and have decided how you wish to vote your shares, please vote your shares promptly so that your shares are represented and voted at the respective company’s special meeting. If you hold your shares in your name as a shareholder of record, you must complete, sign, date and mail your proxy card in the enclosed postage-paid return envelope, or follow the telephone or Internet voting procedures described on the proxy card, as soon as possible. If you hold your shares in “street name” through a bank or broker, you must direct your bank or broker how to vote in accordance with the instructions you have received from your bank or broker. You may also cast your vote in person at the respective company’s special meeting. “Street name” shareholders who wish to vote in person at the respective company’s special meeting will need to obtain a proxy form from the institution that holds their shares.

First Security shareholders are receiving an election form with this joint proxy statement/prospectus. The election form allows First Security shareholders to elect their preferred form of the Merger Consideration. If you wish to make an election, you should complete the election form and send it in the envelope provided to Atlantic Capital’s exchange agent, Computershare. To make an effective election, your properly executed election form must be received by Computershare before the Election Deadline. If you do not return a completed, properly executed election form by the Election Deadline, you will be treated as having made no election and will receive cash or stock or a combination thereof based on the elections made by other First Security shareholders.

A: Atlantic Capital special meeting : The presence at the Atlantic Capital special meeting, in person or by proxy, of holders of a majority of the outstanding shares of Atlantic Capital common stock entitled to vote at the special meeting will constitute a quorum for the transaction of business. Abstentions and broker non-votes, if any, will be included in determining the number of shares present at the meeting for the purpose of determining the presence of a quorum.

First Security special meeting : The presence at the First Security special meeting, in person or by proxy, of holders of a majority of the outstanding shares of First Security common stock entitled to vote at the special meeting will constitute a quorum for the transaction of business. Abstentions and broker non-votes, if any, will be included in determining the number of shares present at the meeting for the purpose of determining the presence of a quorum.

A: Atlantic Capital special meeting : Approval of the Atlantic Capital merger proposal requires the affirmative vote of at least a majority of all of the outstanding shares of Atlantic Capital common stock entitled to vote on the merger as of the close of business on [●], 2015, the record date for the Atlantic Capital special meeting. If you (1) fail to submit a proxy or vote in person at the Atlantic Capital special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote with respect to the proposal to approve the

merger agreement, it will have the same effect as a vote “AGAINST” the proposal. Assuming a quorum is present, approval of the Atlantic Capital adjournment proposal requires the affirmative vote of a majority of the shares of Atlantic Capital common stock present at the special meeting, in person or by proxy and entitled to vote as of the close of business on [●], 2015, the record date for the Atlantic Capital special meeting. If you (1) fail to submit a proxy or vote in person at the Atlantic Capital special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote with respect to the Atlantic Capital adjournment proposal, it will have no effect on such proposal.

First Security special meeting : Approval of the First Security merger proposal requires the affirmative vote of a majority of all of the outstanding shares of First Security common stock entitled to vote on the merger as of the close of business on [●], 2015, the record date for the First Security special meeting. If you (1) fail to submit a proxy or vote in person at the First Security special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote with respect to the proposal to approve the merger agreement, it will have the same effect as a vote “AGAINST” the proposal. Approval of the merger-related compensation proposal and the First Security adjournment proposal each require that the votes cast for the proposal exceed the votes cast against the proposal. If you (1) fail to submit a proxy or vote in person at the First Security special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote with respect to these proposals, it will have no effect on these proposals.

A: If you do not submit a proxy or vote in person, it may be more difficult for Atlantic Capital or First Security to obtain the necessary quorum to hold their special meetings. In addition, your failure to submit a proxy or vote in person, or failure to instruct your bank or broker how to vote, or abstention will have the same effect as a vote against approval of the merger agreement. The merger agreement must be approved by the affirmative vote of at least a majority of the outstanding shares of each of Atlantic Capital and First Security common stock entitled to vote on the merger agreement.

A: If your shares are held in “street name” in a stock brokerage account or by a bank or other nominee, you must provide the record holder of your shares with instructions on how to vote your shares. Please follow the voting instructions provided by your broker, bank or other nominee. Please note that you may not vote shares held in street name by returning a proxy card directly to Atlantic Capital or First Security or by voting in person at your respective company’s special meeting unless you provide a “legal proxy,” which you must obtain from your broker, bank or other nominee.

Under the rules of applicable securities exchanges, brokers who hold shares in street name for a beneficial owner of those shares typically have the authority to vote in their discretion on “routine” proposals when they have not received instructions from beneficial owners. However, brokers are not allowed to exercise their voting discretion with respect to the approval of matters that the securities exchanges determine to be “non-routine” without specific instructions from the beneficial owner. It is expected that all proposals to be voted on at the Atlantic Capital special meeting and the First Security special meeting are such “non-routine” matters. Broker non-votes occur when a broker or nominee is not instructed by the beneficial owner of shares to vote on a particular proposal for which the broker does not have discretionary voting power.

If you are an Atlantic Capital shareholder and you do not instruct your broker, bank or other nominee on how to vote your shares:

If you are a First Security shareholder and you do not instruct your broker, bank or other nominee on how to vote your shares:

A: Atlantic Capital shareholders : With respect to the Atlantic Capital merger proposal, if you (1) fail to submit a proxy or vote in person at the Atlantic Capital special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote, it will have the same effect as a vote “AGAINST” the proposal. With respect to the Atlantic Capital adjournment proposal, if you (1) fail to submit a proxy or vote in person at the Atlantic Capital special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote, it will have no effect on such proposal.

First Security shareholders : With respect to the First Security merger proposal, if you (1) fail to submit a proxy or vote in person at the First Security special meeting, (2) mark “ABSTAIN” on your proxy or (3) fail to instruct your bank or broker how to vote, it will have the same effect as a vote “AGAINST” the proposal. If you fail to submit a proxy or vote in person at the First Security special meeting or fail to instruct your bank or broker how to vote or mark “ABSTAIN” on your proxy with respect to the merger-related compensation proposal or the First Security adjournment proposal, it will have no effect on such proposal.

A: Yes. All shareholders of Atlantic Capital and First Security, including shareholders of record and shareholders who hold their shares through banks, brokers, nominees or any other holder of record, are invited to attend their respective special meetings. Holders of record of Atlantic Capital common stock and holders of record of First Security common stock can vote in person at the Atlantic Capital special meeting and First Security special meeting, respectively. If you are not a shareholder of record, you must obtain a proxy, executed in your favor, from the record holder of your shares, such as a broker, bank or other nominee, to be able to vote in person at the special meetings. If you plan to attend your special meeting, you must hold your shares in your own name or have a letter from the record holder of your shares confirming your ownership. In addition, you must bring a form of personal photo identification with you in order to be admitted. Atlantic Capital and First Security reserve the right to refuse admittance to anyone without proper proof of share ownership or without proper photo identification. The use of cameras, sound recording equipment, communications devices or any similar equipment during the Atlantic Capital or First Security special meeting is prohibited without Atlantic Capital’s or First Security’s express written consent.

A: Atlantic Capital shareholders : Yes. If you are a holder of record of Atlantic Capital common stock, you may revoke any proxy at any time before it is voted by (1) signing and returning a proxy card with a later date, (2) timely submitting a later proxy via the telephone or Internet, (3) delivering a written revocation letter to Atlantic Capital’s corporate secretary or (4) attending the special meeting in person, notifying the corporate

secretary and voting by ballot at the special meeting. Attendance at the special meeting will not automatically revoke your proxy. A revocation or later-dated proxy received by Atlantic Capital after the Atlantic Capital special meeting will be ineffective. Atlantic Capital’s corporate secretary’s mailing address is: 3280 Peachtree Road NE, Suite 1600, Atlanta, Georgia 30305, Attention: Corporate Secretary. If you hold your shares in “street name” through a bank or broker, you should contact your bank or broker if you want to revoke your proxy.

First Security shareholders : Yes. If you are a holder of record of First Security common stock, you may revoke any proxy at any time before it is voted by (1) signing and returning a proxy card with a later date, (2) voting by telephone or the Internet at a later time, (3) delivering a written revocation letter to First Security’s corporate secretary or (4) attending the special meeting in person, notifying the corporate secretary and voting by ballot at the special meeting. Attendance at the special meeting will not automatically revoke your proxy. A revocation or later-dated proxy received by First Security after the First Security special meeting will be ineffective. First Security’s corporate secretary’s mailing address is: 531 Broad Street, Chattanooga, Tennessee 37402, Attention: Corporate Secretary. If you hold your shares in “street name” through a bank or broker, you should contact your bank or broker if you want to revoke your proxy.

A: The merger is intended to qualify as a tax-free “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”). First Security shareholders who receive solely cash in exchange for their First Security common stock will recognize gain or loss for U.S. federal income tax purposes on the shares of First Security common stock exchanged for cash. In general, holders of First Security common stock who receive only shares of Atlantic Capital common stock in the merger are not expected to recognize any gain or loss for U.S. federal income tax purposes, except to the extent of any cash received in lieu of any fractional shares of Atlantic Capital common stock. First Security shareholders who do not elect to receive cash in exchange for their First Security common stock, including both shareholders who make no election and shareholders who elect to receive Atlantic Capital common stock, may nevertheless receive cash in the event that First Security shareholders owning at least 20,041,578 shares of First Security common stock (representing the Cash Election Minimum Threshold of 30% of the total outstanding First Security common stock) do not elect to receive cash in exchange for their First Security common stock. Holders of First Security common stock who receive both cash (other than cash in lieu of fractional shares) and shares of Atlantic Capital common stock in the merger may be required to recognize any gain for U.S. federal income tax purposes, but not in excess of the cash received (in addition to any gain or loss recognized with respect to any cash received in lieu of any fractional shares of Atlantic Capital common stock).

For further information, see “The Merger—Material U.S. Federal Income Tax Consequences of the Merger.”

The U.S. federal income tax consequences described above may not apply to all holders of First Security common stock. Your tax consequences will depend on your individual situation. Accordingly, we strongly urge you to consult your own tax advisor to determine the particular tax consequences of the merger to you.

A: Atlantic Capital shareholders : No, Atlantic Capital shareholders are not entitled to any dissenter or appraisal rights under Georgia law in connection with any of the proposals.

First Security shareholders : No, First Security shareholders are not entitled to any dissenter or appraisal rights under Tennessee law in connection with any of the proposals.

A: No. Please do not send in your First Security stock certificates with your proxy. Atlantic Capital’s exchange agent, Computershare, will send you instructions for exchanging First Security stock certificates for the Merger Consideration. See “The Merger Agreement—Election to Receive Stock or Cash—Letter of Transmittal; Exchange of Shares.”

A: You should return your election form, and follow the instructions provided on the election form, in order to make your election of the Merger Consideration. See “The Merger Agreement—Election to Receive Stock or Cash—Letter of Transmittal; Exchange of Shares.”

A: If you are unable to locate your original First Security stock certificate(s), you should contact First Security’s transfer agent, Computershare, at 10 Commerce Drive, Cranford, New Jersey 07016-3572, or at (800) 368-5948. Following the merger, any inquiries should be directed to Atlantic Capital’s transfer agent, which is also Computershare, at 211 Quality Circle, Suite 210, College Station, Texas 77845, or at (800) 368-5948.

A: Atlantic Capital and First Security expect to complete the merger late in the third quarter or early in the fourth quarter of 2015. However, neither Atlantic Capital nor First Security can assure you when or if the merger will occur. In addition to other customary closing conditions provided in the merger agreement, Atlantic Capital and First Security must first obtain the approval of Atlantic Capital shareholders and First Security shareholders for the merger, as well as the necessary regulatory approvals.

A: Atlantic Capital shareholders : In addition to solicitation of proxies by Atlantic Capital by mail, proxies may also be solicited by Atlantic Capital’s directors and employees personally, and by telephone, facsimile or other means. For more information on solicitation of proxies in connection with the Atlantic Capital special meeting, see “The Atlantic Capital Special Shareholders Meeting—Solicitation of Proxies.”

First Security shareholders : In addition to solicitation of proxies by First Security by mail, proxies may also be solicited by First Security’s directors and employees personally, and by telephone, facsimile or other means. For more information on solicitation of proxies in connection with the First Security special meeting, see “The First Security Special Shareholders Meeting—Solicitation of Proxies.”

A: Atlantic Capital shareholders : If you have any questions concerning the merger or this joint proxy statement/prospectus, would like additional copies of this joint proxy statement/prospectus or need help voting your shares of Atlantic Capital common stock, please contact: Carol H. Tiarsmith, Executive Vice President and Chief Financial Officer, 3280 Peachtree Road NE, Suite 1600, Atlanta, Georgia 30305, (404) 995-6050.

First Security shareholders : If you have any questions concerning the merger or this joint proxy statement/prospectus, would like additional copies of this joint proxy statement/prospectus or need help voting your shares of First Security common stock, please contact: John R. Haddock, Chief Financial Officer, Executive Vice President and Secretary, 531 Broad Street, Chattanooga, Tennessee 37402, (423) 308-2075.

Important Notice Regarding the Availability of Proxy Materials for the Atlantic Capital

Special Shareholder Meeting to be Held on [●] , 2015.

The Notice of Special Meeting and this Joint Proxy Statement/Prospectus are available at:

[●]

Important Notice Regarding the Availability of Proxy Materials for the First Security Special Shareholder Meeting to be Held on [ ● ], 2015.

The Notice of Special Meeting and this Joint Proxy Statement/Prospectus are available at:

[●]