He was elected in 1820 as a Democratic-Republican to the Seventeenth Congress and reelected as a Jackson Democrat to the Eighteenth Congress (March 4, 1821 – March 3, 1825). While in Congress, Johnson served as chairman of the Committee on the Post Office and Post Roads (Eighteenth Congress). He declined to run in 1824.
He was appointed judge of the Kentucky Court of Appeals April 20, 1826, and served until December 30, 1826.
Johnson was ordained as a minister of the Christian Church, where he served for a number of years. He became active in publishing Christian journalism. He became editor of the Christian Messenger in 1832, the Gospel Advocate in 1835, and the Christian in 1837.