He taught school, studied law in Litchfield, Connecticut, was admitted to the bar and commenced practice in Hartford.
He was a justice of the court of common pleas of Hampshire County, and was elected as a Federalist to the Fourth, Fifth, and Sixth Congresses and served from March 4, 1795, until November 6, 1800, when he resigned.
He was previously a candidate for the 4th congressional district in 1788; the election took 5 ballots, and Lyman led on the 2nd and 3rd before losing on the final two to Theodore Sedgwick.
Samuel's sister, Anna Lyman (1746–1842), married Gideon Wheeler (1745–1822), also a veteran of the American Revolution.
They had a daughter, Mary Ann Savage, who married Ward Hunt, United States Supreme Court Justice.