He was educated locally, and trained for a legal career.
Tompkins served as a Private in the 2nd Regiment of Westchester County Militia (Thomas"s Regiment) during the In October, 1776 he abandoned his home and fled British troops, successfully evading capture by submerging himself in a nearby swamp. This incident was known to James Fenimore Cooper, who used a fictionalized version of it in his 1821 novel The Spy. Tompkins remained in the militia after the war, and was a Captain when he resigned in 1797.
He also inherited Fox Meadows, where he resided throughout his life.
He served as Judge of the Westchester County Court from 1807 to 1820. Tompkins was elected to the Fifteenth and Sixteenth Congresses, and served from March 4, 1817 to March 3, 1821.
In 1823 Tompkins returned to the position of Westchester County Judge, and he remained on the bench until his death. In 1828 he was an unsuccessful candidate for Congress, losing a narrow contest to Henry B. Cowles.
Tompkins died in Scarsdale, New York, January 1, 1846.
An Anti-Federalist who became a member of the Democratic-Republican Party and later a Democrat who identified with the Bucktails and Jacksonians, he was Scarsdale"s first Town Clerk, and held other local offices including Town Supervisor. Tompkins was a member of the New York State Assembly from 1804 to 1806.