UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

Amendment No. 1

QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15 (d) OF THE SECURITIES

EXCHANGE ACT OF 1934

FOR THE QUARTERLY PERIOD ENDED September 30, 2018

Commission file number: 000-22507

THE FIRST BANCshARES, INC.

(Exact name of Registrant as specified in its charter)

(601) 268-8998

(Registrant’s telephone number, including area code)

Not Applicable

(Former name, former address and former fiscal year, if changed since last report)

Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15 (d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.

Yes þ                 No ¨

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Yes þ                  No ¨

Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

Yes ¨              No þ

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date.

Common stock, $1.00 par value, 14,864,046 shares issued and 14,837,552 outstanding as of November 7, 2018.

Explanatory Note

The First Bancshares, Inc. (the “Company”) is filing this Amendment No. 1 (this “Amendment”) to its Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018 (the “Form 10-Q”) solely for the purpose of correcting the number of shares of common stock issued and outstanding at November 7, 2018 reported in the cover page.

Except as described above, this Amendment does not reflect events occurring after the filing of the original Form 10-Q and no revisions are being made pursuant to this Amendment to the Company’s financial statements or any other disclosure contained in the Form 10-Q.

PART II

ITEM 6. EXHIBITS

* Filed herewith.

Signatures

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.