He served one term (1859–1861) in the Tennessee House of Representatives, where he was one of the few state legislators to oppose secession on the eve of the Civil War.

He represented Hamilton County at the pro-Union East Tennessee Convention, and afterward fought for the Union Army.

[4] Running on the pro-Union Opposition Party ticket,[5] Trewhitt was elected to Hamilton County's seat in the Tennessee House of Representatives in 1859.

Trewhitt was elected to Hamilton County's seat in the Tennessee Senate in August 1861, but the state having seceded, he instead fled to Kentucky to join the Union Army.

[1] During the Confederate crackdown following the East Tennessee bridge burnings in late 1861, Trewhitt's father, Levi, was arrested and jailed on suspicion of aiding the bridge-burners.

He afterward supported the agenda of Brownlow and the Radical Republicans, including a contentious piece of legislation known as the "franchise bill," which barred ex-Confederates from voting.

[10] In 1864, Johnson appointed Trewhitt chancellor (judge) of the state's second chancery division, which included Chattanooga and surrounding areas of southeastern Tennessee.

He held this position until 1870, when the new state constitution restored the voting rights of former Confederates, and he was defeated in his bid for reelection by David M.

[11] During this period, Trewhitt staunchly supported prohibition, going so far as to state, "the greatest battle of the age is now being fought, headed on the one side by Satan in the form of intoxicating liquor, on the other hand by Christianity, morality, sobriety, and decency.