Johnson was nominated by President Woodrow Wilson on October 1, 1917, to a seat vacated by William LeBaron Putnam. He was confirmed by the United States Senate on October 1, 1917, and received commission the same day. Assumed senior status on April 30, 1929. Johnson's service was terminated on February 15, 1930, due to death.
Johnson was elected as a Democrat to the United States Senate in 1910 and served from March 4, 1911, until March 3, 1917.[2] He was an unsuccessful candidate for reelection in 1916.[2] He was Chairman of the Committee on National Banks (63rd United States Congress), Committee on Fisheries (64th United States Congress) and the Committee on Pensions (64th United States Congress).[2]