He was general counsel to the Farm Credit Administration in Omaha from 1931 to 1933, returning to private practice there from 1934 to 1938.
On Nov. 28, 1938, he was appointed by Governor Robert Leroy Cochran to be an associate justice of the Supreme Court of Nebraska.
Johnsen's term began January 3, 1939, lasting until he resigned November 8, 1940.
[1] Johnsen was nominated by President Franklin D. Roosevelt on October 1, 1940, to the United States Court of Appeals for the Eighth Circuit, to a new seat authorized by 54 Stat.
[1] He served as Chief Judge and as a member of the Judicial Conference of the United States from August 7, 1959 to July 16, 1965.