He was a member of the Washington State Legislature, was mayor of Klamath Falls, Oregon, and three times was a candidate to represent Oregon in the United States Senate, losing to Charles L. McNary in 1936, Rufus Holman in 1938, and Guy Cordon in 1944.

Mahoney also supported the Townsend Plan, a proposal presented by Francis Townsend for a national sales tax to pay for a $200 monthly pension for everyone over age 60.

"[citation needed] The election was close, but McNary was reelected.

One year after his defeat, Mahoney was charged with reckless driving in an incident that killed Thomas L. Zimmerman of Shedd.

Still, he lost the race 57-42% to Holman, and was defeated for yet another run for the Senate in 1944, by Guy Cordon.