Mäenpää started his senior career with the club, making his first competitive appearance on 23 May 2014 in a 1-0 home victory in the league over Tampereen-Viipurin Ilves-Kissat.[2] He was subbed on for Juho Saarinen in the 68th minute.
Haka
In January 2015, Mäenpää moved to Ykkönen club FC Haka. He made his league debut for the club on 2 May 2015, playing all ninety minutes in a 2-2 away draw with JJK.[3] He scored his first competitive goal for the club on 2 August 2015 in a 4-3 away victory in the league over MP.[4] His goal, scored in the 69th minute, made the score 4-1 to Haka.
Inter Turku
In November 2017, Mäenpää moved to Veikkausliiga club Inter Turku, arriving alongside Mikko Kuningas.[5] He made his league debut for the club on 7 April 2018 in a 2-0 away defeat to VPS, playing 63 minutes before being subbed off, to be replaced by Arttu Hoskonen.[6]
IFK Mariehamn
On 28 November 2019 it was confirmed, that Mäenpää would join IFK Mariehamn from the 2020 season, signing a deal until the end of 2021.[7]
Warta Poznań
On 22 December 2021, Mäenpää penned a two-and-a-half-year deal with Polish Ekstraklasa club Warta Poznań, effective from 1 January 2022.[8][9] He was released by the club at the end of the 2023–24 season.[10]
Halmstad
On 15 July 2024, Swedish Allsvenskan club Halmstad announced the signing of Mäenpää.[11] He scored his first Allsvenskan goal on 19 October, in a 3–1 home win against Sirius.
Personal life
Mäenpää's twin brother Aapo is also a professional footballer.[12] The two played together in their early years at Hämeenlinna and Haka, before reuniting at Mariehamm beginning in 2020.