Simmonds spent his major junior career playing two seasons in the OHL from 2006 until 2008 with the Owen Sound Attack and Sault Ste. Marie Greyhounds. He also played for Canada at the 2008 World Junior Ice Hockey Championships. While playing with the Jr. Canadiens, Simmonds became friends with Chris Stewart. The two would later purchase a house together in Toronto, where they lived during the off-season.