Three-year men formed into a battalion of three companies (A, B, and D) and assigned to duty at Headquarters XII Corps April 26 as the 10th Maine Infantry Battalion. Old members mustered out May 8, 1863, at Portland, Maine. Chancellorsville Campaign April 27-May 6. Battle of Chancellorsville May 1–5. Gettysburg (Pa.) Campaign June 13-July 24. Provost duty at Battle of Gettysburg July 1–3. Along the Rapidan August 1-September 24. Moved to Nashville, Tenn., September 24-October 2; to Murfreesboro, Tenn., October 5, thence to Shelbyville and Wartrace. Reopening Tennessee River October 26–29. Provost duty at Headquarters XII Corps until February. Detached from XII Corps at Tullahoma, Tenn. February 29, 1864, to be amalgamated with the 29th Maine Infantry, which occurred May 29, 1864, at Morganza, La.