Erickson was Richland County District Attorney from 1936 to 1938 and was an Associate Justice of the Montana Supreme Court from 1939 to 1945. He was a delegate to the Democratic National Conventions in 1948, 1952, and 1956. In 1944, he ran for Governor of Montana, winning the Democratic primary and advancing to the general election, where he opposed Republican incumbent Gov. Sam C. Ford. Ford ended up defeating Erickson by a wide margin to win his second term as governor. Erickson challenged incumbent Sen. Burton K. Wheeler in the Democratic primary in 1946, and though he ended up defeating Wheeler in an upset, he lost the general election to Republican State Senator Zales Ecton. He ran for governor once more in 1948, but finished third in the Democratic primary behind former Montana Attorney General John W. Bonner and Arthur Lamey. From 1956 to 1958 he was chairman of the Montana Democratic Party and from 1962 to 1973 he was a member of the Democratic National Committee.