Markus Mustajärvi (born 24 February 1963) is a Finnish politician for the Left Alliance.

He graduated as ylioppilas in 1982, forestry engineer in 1988 and Master of Social Sciences in 1993, the last degree being from the University of Jyväskylä.

[1] On 30 June 2011, Mustajärvi and fellow MP Jyrki Yrttiaho were expelled from the Left Alliance parliamentary group because they had voted for a motion of no confidence against the Katainen Cabinet in which the Left Alliance was represented.

[2] Mustajärvi and Yrttiaho founded a new opposition parliamentary group called the Left Faction in September 2011.

After the 2015 election, Mustajärvi was allowed to return to the Left Alliance parliamentary group.