During the American Civil War, he served as a Union Army officer and was on the staff of General William Tecumseh Sherman.
[2] In July 1862, Treat volunteered for service in the American Civil War and was appointed first lieutenant of Company B in the 31st Wisconsin Infantry Regiment.
[3] They mustered into federal service in December 1862 and went forward to Tennessee, where they spent the next 18 months guarding supply routes.
[4] After returning to Wisconsin, Treat was engaged in a mercantile business and served as foreman of the engine company 1 of the Monroe volunteer fire department.
Treat was involved in the Republican Party and was elected to the Wisconsin State Assembly in 1894, representing all of Green County.
[2] After his term in the Assembly, Treat was appointed to the State Board of Control by Governor Edward Scofield.
Joseph's son, Charles Treat, became a major general in the United States Army after commanding a division in World War I.