Undrafted, Kemppainen played nine seasons in the Finnish Liiga with Ässät, HPK and Oulun Kärpät.[1] After his second consecutive season of 30 plus points with Kärpät in the 2014–15 season, on 21 May 2015, Boston Bruins general manager Don Sweeney announced that the club had signed Kemppainen to a one-year, two-way NHL contract for the 2015–16 season.[2]
He picked up his first NHL assist and scored his first NHL goal on 23 October 2015, against Jaroslav Halák of the New York Islanders in a 5-3 Bruins victory.
Less than a year after coming to the United States, Kemppainen signed a deal with KHL hockey club Sibir Novosibirsk on 14 May 2016.[3]
Following two productive seasons with Salavat Yulaev Ufa, including reaching the Eastern Conference Finals in the 2018–19 season, posting 14 points in 17 games, Kemppaninen secured a lucrative one-year contract with SKA Saint Petersburg on 1 May 2019.[4]
Kemppaninen played three seasons with SKA Saint Petersburg before leaving following the 2021–22 campaign to return to his native Finland on a one-year contract with former club, Kärpät of the Liiga, on 27 April 2022.[5]