He attended the common schools and Lafayette College in Easton, Pennsylvania, from 1842 to 1844.
He moved to Mount Bethel, Pennsylvania, in 1839. He was a plantation tutor in Mississippi from 1844 to 1846. He returned to Pennsylvania, studied law, and attended Union Law School in Easton.
He was admitted to the bar in 1848 and commenced practice in Easton.
He served as county court clerk from 1848 to 1853. He served as revenue commissioner of the third judicial district in 1859 and 1860.
He was a delegate to the 1864 Democratic National Convention. Johnson was elected as a Democrat to the Thirty-seventh, Thirty-eighth, and Thirty-ninth Congresses and until his death in Washington, District of Columbia Interment in Easton Cemetery.
He was a member of the Pennsylvania House of Representatives in 1853 and 1854.