[3] While overseeing his private practice, Johnson simultaneously lectured in Political Science and Law at the University of North Dakota.

[6][7] Following the recall of William Lemke, Johnson, after receiving the endorsement of the Independent Voters Association, was elected North Dakota Attorney General in 1921.

In 1922 he was elected justice of the North Dakota Supreme Court, defeating the incumbent James Robinson.

[8][1] On December 1, 1926, Johnson resigned from the North Dakota Supreme Court and became legal counsel and Professor of Law at the University of Illinois at Urbana-Champaign.

He was survived by his wife Esther Slette of Manchester, Minnesota and his son Paul, who served as a captain in the United States Army during World War II.