A product of local KuPS, Pennanen made his senior début on 29 April 2007, aged 16, against VIFK. A month later, he was a starter against PK-35. That season he appeared in 13 first-team matches. In February 2009 Pennanen signed a two-year contract with the Dutch team FC Twente along with teammate Tuomas Rannankari.
After not making a single appearance for the FC Twente's first-team, Pennanen left the Dutch champions during winter 2011 and signed with TPS. He signed with RoPS before the 2014 season.