Harmon was the head coach for the Gonzaga Bulldogs men's basketball team from 1913 to 1915.
[1] In 1917, Harmon returned to his alma mater, Illinois College in Jacksonville, Illinois, to become head football coach, succeeding his brother, William T. Harmon, who was serving as a captain in the United States Army at Camp Grant near Rockford, Illinois.
While he was coaching at Gonzaga, Harmon also practiced law with the offices of Luby and Pierson.
At Santa Clara, he taught law as a member of the faculty.
In 1930, Harmon passed the Illinois state bar and began a law practice in Jacksonville, Illinois.