A product of local
Kuopion Palloseura (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
Twente along with teammate
Tuomas Rannankari. After not making a single appearance for the Twente's first-team, Pennanen left the Dutch champions during winter 2011 and signed with
TPS. He signed with
RoPS before the
2014 season. On 14 January 2020, Pennanen left
KuPS and signed a contract with
Indonesian Liga 1 club
Persikabo 1973. In 2021, Pennanen joined
USL Championship side
Sacramento Republic. Pennanen was released by Sacramento following the 2021 season. On 14 December 2021, he signed a three-year contract with
Ilves. On 23 July 2023,
Indian Super League club
Hyderabad announced the signing of Pennanen on a one-year deal. In February 2024, Pennanen terminated his contract with Hyderabad due to unpaid salaries. On 28 February 2024, Pennanen returned to Finland and
Kuopio after signing a one-year deal with his hometown club
KuPS, with an option to extend for one more, reuniting with his former coach
Jani Honkavaara. On 24 July, his deal was extended for the 2025. On 21 September, Pennanen helped his team to win the
2024 Finnish Cup title by scoring a brace in the final in a 2–1 win against
Inter Turku. On 19 October, Pennanen scored the winning goal in the last match of the season against
HJK Helsinki, helping his side secure the
Veikkausliiga championship title and completing the club's first-ever double. ==International career==