John Harmon was born in 1935 in Oshkosh, Wisconsin. He began playing piano at a young age with his mother, who played mostly by ear. She taught him the basics, and the two harmonized tunes together. His exposure to jazz came early, too, thanks in part to his father's extensive collection of jazz records, which included recordings of such greats as Duke Ellington, Teddy Wilson, and Art Tatum.
Harmon graduated from Lawrence University in 1957 with a degree in music composition. The summer after graduation, Harmon attended the first session of the Lenox School of Jazz - the legendary summer program recognized as one of the first educational programs with a jazz curriculum. Harmon studied with Oscar Peterson, whom he credits with improving his playing immensely.
A widely commissioned composer, Harmon has written music for the Milwaukee Symphony Orchestra, "The Orchestra" of Los Angeles, the Fox Valley Symphony and the Santa Fe Chamber Orchestra. His music contains elements of jazz, as well as Americana and Native American influences.