Mullinder was drafted in the fourth round, 31st overall, by the Saskatchewan Roughriders in the 2004 CFL Draft and would go on to play for eight seasons with the team. He won a Grey Cup championship with the team in 2007. He was traded to the Alouettes on August 8, 2011 for import receiver Dallas Baker and was released by the Alouettes on August 22, 2011. He was signed by the Hamilton Tiger-Cats on August 23, 2011 and released the following off-season on February 1, 2012. He was re-signed by the Alouettes on March 26, 2012. On April 30, 2013, Mullinder signed a one-day contract with Saskatchewan so that he could retire as a member of the Roughriders.