Following Dion's resignation, Marissen supported Michael Ignatieff for Liberal Party leader. Ignatieff was confirmed as Leader at a national convention in Vancouver in late April 2009. In the most recent federal Liberal leadership contest, Marissen was campaign manager for George Takach for Liberal Party leader. After Takach withdrew from the contest, Marissen joined him in supporting Justin Trudeau. Marissen was very involved in BC Premier Christy Clark's successful campaign in the 2013 BC provincial election. More recently, Marissen served as strategist for Michael Lee's campaign for the leadership of the BC Liberal Party, where Mr. Lee was 30 points short from being on the final ballot. In July 2018, Mark helped to create YES Vancouver, a new "YIMBY" municipal political party devoted to solving Vancouver's housing crisis by focusing on zoning reform. YES Vancouver ran candidates for council, school board and park board. Hector Bremner, a councillor for the Non Partisan Association of Vancouver, ran for Mayor under the YES banner, but only took 5.73% of the vote.