Senator Humphrey was elected to a third term. Humphrey resigned on December 29, 1964 after winning election to the Office of Vice President of the United States on November 3, 1964. DFLer Walter Mondale was appointed to the U.S. Senate on December 30, 1964 for the unexpired term ending January 3, 1967 to fill the vacancy caused by the resignation.
Peterson was a resident of Minneapolis, former Chair of the Minnesota Republican Party (1950-1953), sitting state Representative (HD 34, 1947-1955), nominee for the Railroad and Warehouse Commission in 1964, and Railroad and Warehouse Commissioner (1967-1972).
Feingold was a resident of Minneapolis and Twin Cities organizer for the Socialist Workers Party. He was nominated by petition.