Sumusalo began his senior club career playing for Klubi-04, before making his league debut for HJK at age 19 in 2009.

After starting his footballing career at his local FC Futura, the nine-year-old defender moved to HJK in 1999.

After coming through the junior levels and the reserves, Sumusalo made his first division debut on 25 May 2009 against FC Lahti.

For the 2018 season, Mikko Sumusalo returned back to HJK Helsinki to play in the highest Finnish football league.

[10] After a four-year stint with IFK Mariehamn in Veikkausliiga, Sumusalo moved to Kotka and signed with Kotkan Työväen Palloilijat (KTP) for the 2024 Ykkösliiga season in Finnish second-tier.