Peck joined the Vermont National Guard after the Civil War and served in various command and staff positions, attaining the rank of lieutenant colonel.
 From 1870 to 1872 Peck served as chief of staff to Governor John Stewart with the rank of colonel.
 He was subsequently appointed commander of the Vermont National Guard's 1st Infantry Regiment.

Peck succeeded James Stevens Peck (no relation) as Adjutant General of the Vermont National Guard with the rank of brigadier general, and served from 1881 to 1901, later receiving promotion to brevet major general to recognize his superior performance.
Peck joined the Vermont National Guard after the Civil War and served in various command and staff positions, attaining the rank of lieutenant colonel.  From 1870 to 1872 Peck served as chief of staff to Governor John Stewart with the rank of colonel.  He was subsequently appointed commander of the Vermont National Guard's 1st Infantry Regiment.
Peck succeeded James Stevens Peck (no relation) as Adjutant General of the Vermont National Guard with the rank of brigadier general, and served from 1881 to 1901, later receiving promotion to brevet major general to recognize his superior performance.
Theodore S. Peck