FC Jyväskylä Blackbird Markkanen made his debut on senior level in
Blackbird in season 2010.
Vihtavuoren Pamaus For season 2011 he played for Vihtavuoren Pamaus in the Finnish
Kakkonen.
JJK Jyväskylä In 2012 he returned to
JJK and made his
Veikkausliiga debut.
AIK Fotboll In December 2013 it was announced that
AIK had signed Markkanen on a three-year contract.
Real Madrid On 23 July 2014,
Real Madrid signed Markkanen from
AIK on a four-year contract. In September 2014, he was chosen for
Real Madrid's 25-man squad for the
UEFA Champions League, but did not make any appearances. On 21 August 2015, Real Madrid released Markkanen. There were rumours of him reporting back to preseason training overweight, but the club never released an official statement about the issue.
Real Madrid Castilla Markkanen made his debut for Real Madrid's reserve team
Real Madrid Castilla in
Segunda División B on 24 August 2014, playing the full 90 minutes as they lost 2–1 at
Atlético Madrid B in Segunda División B Group 2. Six days later he scored his first goal for the club, in a 1–2 home loss to
Getafe B. However, he missed most of the 2014–2015 season due to injury.
Rovaniemen Palloseura On 3 September 2015, Markkanen was acquired by the Finnish side
RoPS for the remainder of the season after failing to sign for AIK who were rejected a request for an exemption to sign him outside of the transfer window by the
Swedish Football Association.
Return to AIK On 5 November 2015, he signed a three-year contract with AIK. He told the club homepage that he was "Very happy to be back at AIK". On 4 August 2017, Markkanen joined
2. Bundesliga side
Dynamo Dresden on loan for the season, while Dynamo Dresden secured an option to sign him permanently. On 15 January 2018, Markkanen broke his contract with
Dynamo Dresden and went on to join
Danish Superliga side
Randers on loan from
AIK for the rest of the
2017-18 season. He returned to AIK in late June 2018, but left the club by mutual consent on 10 August 2018.
Dalkurd FF On 10 August 2018, Markkanen signed with
Dalkurd in Allsvenskan.
PSM Makassar On 14 January 2019 it was announced that Markkanen would join
PSM Makassar in
Liga 1.
FC Haka On 7 February 2020 Veikkausliiga side
Haka announced that Markkanen would be joining the club on a one-year contract.
Orange County SC On 25 December 2020, it was announced that Markkanen would join
USL Championship side
Orange County ahead of their 2021 season.
HIFK Fotboll On 28 February 2022, Markkanen signed with
HIFK. ==International career==