Lyman was born in Northampton, Massachusetts to Captain William and Jemima (Sheldon) Lyman. He graduated from Yale College in 1776. He was a militia veteran of the American Revolution. During Shays' Rebellion he was an aide to General William Shepard with the rank of major.
In about 1781, Lyman married Jerusha Welles, of East Hartford, Connecticut; they had eight children. Jerusha died at age 43, on June 11, 1803. Lyman served in the Massachusetts House of Representatives in 1787 and in the Massachusetts State Senate in 1789.
Lyman was a candidate for the first congress and ran in the Hampshire Berkshire District as an Anti-Federalist against the Federalist candidate Theodore Sedgwick. Sedgwick was elected. Seventeen towns that were favorable to Lyman were late in sending in their returns; had these towns reported in a timely manner, Lyman would have been elected.
- United States Congress. "William Lyman (id: L000530)". Biographical Directory of the United States Congress.
- William Lyman at Find a Grave
- Dexter, Franklin Bowditch (1903), Biographical sketches of the graduates of Yale college with annals of the College History Vol. III, New York, NY: Henry Holt and Company, pp. 619–620.
- Stephens, Frank Fletcher (1909), The transitional period, 1788-1789, in the government of the United States, Columbia, MO: E. W. Stephens Publishing Company, p. 59.
|U.S. House of Representatives|
| Member of the U.S. House of Representatives
from Massachusetts's 2nd congressional district
March 4, 1793 - March 3, 1797
alongside: Dwight Foster, Theodore Sedgwick, Artemas Ward on a General ticket (1793-1795)
|| United States Consul to London
January 11, 1805 – September 22, 1811