The Honourable Karen Casey was first elected to the Nova Scotia House of Assembly as the Progressive Conservative MLA for Colchester North in 2006 and was re-elected in 2009. She was elected again as a Liberal MLA for Colchester North in 2013 and 2017. 

She was the Interim Leader of the Progressive Conservative Party of Nova Scotia from June 24, 2009 until August 16, 2010 and has served as Minister of Education and Minister of Health.

She resigned from the PC Caucus and joined the Liberal Caucus on January 10, 2011. Under the Liberal Caucus, she has served as Deputy Premier, Minister of Finance and Treasury Board,  Minister responsible for Youth, Minister of Education and Early Childhood Development, and Chair of Treasury and Policy Board.

Karen Casey is a former Assistant Superintendent of the Chignecto-Central Regional School Board and a former principal.