Mars began his musical training at Sykes Music in Brantford, Ontario where he studied the drums with Carl Lemke. In the late 1960s he played the drums in the band John Mars and the Martians with Bassist Kevin Cosman and Guitarist Stan Baka. The group disbanded after Baka was killed by a drunk driver. Mard then moved to Toronto where he met Pianist Stuart Broomer and Saxophonist Bill Smith. The three men formed the successful jazz trio "Broomer, Mars & Smith" which actively performed throughout the 1970s. In 1980 Smith left to pursue other projects and the duo "Stuart Broomer & John Mars" was formed. The duo performed up through 1986 and notably released the 1983 album, Annihilated Surprise, on Ugly Dog Records.