Parker was a member of the New Hampshire House of Representatives from 1794 to 1804 and in 1806–1807; in 1804 and 1805 he was a member of the Governor's council. He was elected as a Democratic-Republican to the U.S. Senate and served from March 4, 1807, to June 1, 1810, when he resigned.
From 1807 to 1813, Parker was a justice of the Court of Common Pleas for Cheshire and Sullivan Counties. He was associate justice of the western circuit from 1813 to 1816 and a judge of the court of sessions of Cheshire County in 1821 and of the court of common pleas of Hillsborough County in 1822. He was a member of the New Hampshire Senate and its president in 1828.