She was previously a member of the Legislative Assembly (MLA), representing Vancouver-Mount Pleasant from 1996 to 2015 with the British Columbia (BC) NDP, and was a provincial cabinet minister from 1998 to 2001.

In 2001, Kwan, along with Joy MacPhail, was one of only two NDP MLAs to survive the party's electoral collapse in the 2001 British Columbia general election due to a BC Liberal landslide upset.

In December 2010, Kwan released a statement to the media criticizing NDP leader Carole James, and calling for an immediate leadership convention, after party candidates suffered defeat in the 2009 election.

[4][6][7] In response to Kwan's statement, James called an emergency caucus session to address opposition to her continued leadership.

[21] Supporters of Kwan's candidacy included Union of British Columbia Indian Chiefs president Stewart Philip, Chinese Freemasons Association president Herbert Yiu, former British Columbia natural resources minister Robert Arthur Williams, and United Steelworkers official Steve Hunt.

She was elected to the House of Commons in October 2015, defeating candidates Edward Wong (Liberal) and James Low (Conservative) by wide margins.