Seth C. Farrington was born around 1836 in Maine to Noyes and Mary Farrington. His father was a farmer who owned $2,500 of real estate and $400 of personal property by 1860. He grew up and attended school in Fryeburg, Maine, and by 1860, he was working as a farmer.
On November 15, 1861, he received a commission as a captain in Company F of the 12th Maine Infantry. The regiment took part in the siege of Port Hudson. He was promoted to major in September 1864, and he served as a Judge Advocate and an acting assistant adjutant general. He mustered out on May 31, 1866.
He returned to Fryeburg after leaving the army, and he worked as a railroad engineer. He died sometime after 1874.