Marilyn has served as a Toronto City Councillor, Member of Provincial Parliament, provincial Cabinet Minister, and Deputy Leader of the Ontario New Democratic Party. She was also the first female Deputy Speaker of the Ontario Legislature. Before her time in public office, she held a number of senior positions in the not-for-profit sector including Executive Director of the Canadian Environmental Defence Fund, director of the Co-op Housing Federation of Toronto, and co-founder of the Bain Avenue Day Care Centre. She has written articles, op-ed pieces, and book reviews for many publications including the Toronto Star, the Globe and Mail, the Toronto Sun, and Now Magazine. In 2015, Marilyn published a memoir called Shameless: The Fight for Adoption Disclosure and the Search for My Son (Between the Lines, 2015) about her personal and political experiences with adoption and adoption information disclosure legislation. 

Marilyn is currently a Justice of the Peace in Ontario, and resides in Leslieville in Toronto with her devilishly good-looking husband Richard Barry.