A 31 year old McCarthy campaigned for the position of Tenth District Judge in 1939. He defeated incumbent Edgar Werner, becoming Wisconsin's youngest man ever elected circuit court judge. Lawyers praised McCarthy for his speedy judicial rulings and his willingness to travel to the District's courtrooms in Shawano, Langlade, and Outagamie counties.

• Judge McCarthy treated first offenders with leniency and expedited divorce cases.
  
  
• The Wisconsin Supreme Court criticized Judge McCarthy for destroying a court record in 1941. McCarthy had removed one page from a court transcript to hide his comment that a trial in the Quaker Dairy case was a "waste of the court's time." The Department of Agriculture had brought suit against the Quaker Dairy Company for undercutting competition.

Zeke, 1945
Courtesy of a McCarthy family member

Family legend says that McCarthy won Zeke in a poker game. Outagamie County Jail employees made the English bulldog its mascot and gave him the title of deputy sheriff in 1944.