From 1945 to 1978, Harmon was the head professional at Winged Foot Golf Club in Mamaroneck, New York, and also served as the winter professional for many years at the Seminole Golf Club in Juno Beach, Florida. In 1959, he was hired as the head professional at Thunderbird Country Club in Rancho Mirage, California, where he served for over a decade, and finally took a club job in Texas in the Houston area. In 1959, Harmon played in the U.S. Open at Winged Foot and placed third. He was one of the few close friends of legendary star Ben Hogan, and the two played together frequently and worked together on their games.