Thad McArthur attended the University of Washington, graduating with a degree in industrial management in 1950. He swam the 100, 220, and 440 yard freestyle and was a four-year letterman. The Korean War soon began and McArthur was drafted. While in the Army he started training with the modern pentathletes, and his swimming and running ability separated him and he made the 1952 Olympic team, which he considered an upset. After his Olympic appearance, McArthur left the service and spent 40 years working for Sears as an executive. He and his wife later retired to Whidbey Island on the Puget Sound in Washington State.