A native of Antigonish, MacDonald graduated in 1979 with a MSW from the Maritime School of Social Work at Dalhousie University. She was employed as a social worker at the Nova Scotia Hospital (Adolescent Services) and later was a faculty member at her alma mater where she taught social policy and community development. MacDonald also worked at Dalhousie Legal Aid, the North End Clinic and the North End Parent Resource Centre.
MacDonald sought the leadership of the NS NDP in 2000, finishing a strong third.
On June 19, 2009 MacDonald was appointed to the Executive Council of Nova Scotia where she served as Minister of Health as well as Minister of Health Promotion and Protection.[4] On May 30, 2012, Premier Darrell Dexter shuffled his cabinet, appointing MacDonald as Minister of Finance.[5] On May 10, 2013 MacDonald was appointed Minister of African Nova Scotia Affairs.[6]
MacDonald was one of only seven NDP MLAs returned in the 2013 provincial election in which the Dexter government was defeated. On November 16, 2013, it was announced that MacDonald would become the party's interim leader when Dexter steps down as leader on November 23, 2013.[7]
On April 12, 2016, MacDonald announced she was resigning as MLA.[8]