He eventually became a hatter in Troy, New York. There has been speculation that the use of mercury as part of the hatter's trade was a cause of Corbett's later mental problems.
He married but his wife died in childbirth. After his wife's death, he moved to Boston and continued working as a hatter. He became a reborn evangelical Christian and changed his name to Boston. Trying to imitate Jesus, he began to wear his hair very long.
On July 16, 1858, in order to avoid the temptation of prostitutes, Corbett castrated himself with a pair of scissors. Afterwards he went to a prayer meeting and ate a meal before going for medical treatment.
Corbett joined the Union army at the outbreak of the American Civil War. He re-enlisted three times. His final rank was sergeant in the 16th New York Cavalry. He was captured by the Confederate Army on June 24, 1864, and was held captive at Andersonville Prison. He was eventually released and returned to his unit.
On April 24, 1865, he was selected as one of the 26 cavalrymen to pursue John Wilkes Booth after his assassination of Abraham Lincoln. On April 26 they cornered Booth and fellow conspirator David Herold in a tobacco barn on the Virginia farm of Richard Garrett.
The barn was set on fire. Herold surrendered but Booth remained inside. Corbett was positioned by a large crack in the barn wall. He saw Booth moving about inside and shot him with a Colt revolver from a distance of several yards. Booth died a few hours later as Corbett's shot had hit his spinal cord.
Corbett was immediately arrested for disobeying orders but the charges were dropped by Secretary of War Stanton. Later Stanton said, "The rebel is dead. The patriot lives." Corbett duly Corbett received his share of the reward money which amounted to $1,653.85.
In his official statement, Corbett claimed he shot Booth because he thought Lincoln's assassin was getting ready to use his weapons. This was denied by other witnesses.
Shortly thereafter, Corbett returned to being a hatter, first in Boston and later in Connecticut and New Jersey.
His later life was not well documented, but there are a number of stories regarding his increasingly erratic behavior:
The number of references to Corbett pulling a gun on his friends, or waving a gun before a crowd, suggests that Corbett became something of a legend, casting some doubt on the veracity of such stories.
There is a Boston Corbett roadside monument just outside of Concordia, Kansas.