Born in Amos, Quebec, she received a Bachelor of Arts degree from Mount Allison University and a Bachelor of Social Work from the University of Toronto. She is the founding member of the Muriel McQueen Fergusson Foundation for the elimination of family violence. From 1994 to 1997 she was the Lieutenant Governor of New Brunswick.
She was married to the late billionaire entrepreneur Wallace McCain, who co-founded McCain Foods Limited. She has four children and nine grandchildren.
In 2007, St. Thomas University named its newest academic building in her honour. Margaret Norrie McCain Hall, housing a theatre, study lounge, administration offices and classrooms.