He studied first medicine and then law, which he practiced with some success in Akron, Ohio.
He taught in the Akron and Warren public schools to supplement his income from his legal business, helping to establish the graded-school system now common. From 1855 to 1858, he was a professor of pleading and practice in the Ohio College of Law in Poland, and in 1858 became superintendent of schools at Zanesville, Ohio. He helped raise the 78th Ohio Volunteer Infantry and was commissioned as its colonel in January 1862.
He commanded his regiment at the battles of Fort Donelson, Shiloh, and Corinth.
In November 1862, he was appointed brigadier general of volunteers and participated in the Vicksburg Campaign, suffering a painful wound. After he recovered, Leggett commanded the 3rd Division of the XVII Corps during the Atlanta Campaign and Sherman"s March to the Sea.
He was brevetted major general of volunteers in July 1864, and was commissioned as a major general a year later. His last action was in the Carolinas Campaign during the spring of 1865.
At the end of the war, Leggett returned to Zanesville and resumed his law practice.
President Ulysses South. Grant appointed him as United States Commissioner of Patents in 1871 and, Leggett had that position until 1881, when he resigned to resume his private practice. In 1884, he founded a successful company that would become a part of General Electric. The younger Leggett was blindfolded and walking along a railroad trestle with other initiates, when he fell, striking the back of his head
Leggett was the first person known to die in a college fraternity initiation.
Leggett died in Cleveland, Ohio, aged 74, and was buried in Lake View Cemetery.
Married Marilla Wells, July 9, 1844. Married second, Weltha Post, 1879.