The 129th Pennsylvania Infantry was organized at Camp Curtin near Harrisburg, Pennsylvania, and mustered in August 15, 1862 under the command of Colonel Jacob Gellert Frick.

The regiment was attached to 1st Brigade, 3rd Division, V Corps, Army of the Potomac.

Moved to Washington, D.C., August 16, and duty there until September 12.

Moved to Sharpsburg, Md and duty there until October 30.

Burnside's 2nd Campaign, "Mud March," January 20–24, 1863.