 Of his early life little is known except that he was a teacher in his hometown school district.He was commissioned captain of Company G, 4th Vermont Infantry, on September 21, 1861, promoted major on July 18, 1862, lieutenant colonel November 5, 1862 and colonel on February 3, 1864, replacing Charles B. Stoughton, who had resigned.According to Vermont's military historian, George Benedict, Foster was "of stalwart proportions, and handsome face and figure, he was one of the finest looking officers in the brigade.