Trigg's political service started around 1781 when he became a Justice of the Peace in Bedford County. He was elected to represent the county in the Virginia House of Delegates, and served there from 1784 until 1792. In 1788 he represented Bedford County in the Virginia Convention that ratified the U.S. Constitution. Trigg voted with Patrick Henry and the Antifederalists against ratification. He served in the Virginia Senate from 1792 until 1796. He was elected in the United States House of Representatives in 1796 as a Jeffersonian Republican. Trigg was re-elected three times, and served in the Congress from 1797. He died at home on May 17, 1804, on his farm near Liberty in Bedford County and was buried in a family plot there.