Born and living in Richmond Hill, Ontario, Mag is a graduate of the University of Toronto, where she majored in Physical Education. Shortly after graduating she auditioned for a part in a dinner theatre production of Hello Dolly, and later won The du Maurier Search for the Stars. Her first screen role was in the 1980 film Murder by Phone. She has also appeared in two Perry Mason movies, and many Anne fans recognize her as Alice Lawson in the first two Anne movies. Before Road to Avonlea her other roles included Reckless Disregard and Alex: The Life of a Child, as well as the role of a "hot nurse" in Looking for Miracles.

Mag had gotten the call to audition for the role of Aunt Olivia just as she was getting ready to move to California in the summer of 1989. She got the part and ended up returning to Ontario to start shooting. A few months after that, she went back to California and met her then-future husband Daniel Hunter at a party. Three weeks later, they were married; and for the entire seven-year run of the series, she commuted back and forth from California to Ontario. As well, she received two Gemini nominations for the role--one in 1996 for the series, and another one in 1999 for reprising the role in Happy Christmas, Miss King.

In the later part of the 1990s, Mag had a role in the TV movie Shadow Lake and provided the narration for the animated short film My Grandmother Ironed the King's Shirts. She has also hosted three shows for Canada's Women's Television Network--A Repair to Remember (which lasted five years), Men on Women, and the on-going Anything I Can Do (which earned her two Gemini nominations in 2002--one for the series itself, and another for hosting it). More recently, Mag was involved with the reality series Raging Hormones for the CBC.

A licensed carpenter, she also has her own column in the Toronto Star, which also runs in various other newspapers across Canada and the United States. As well, she's involved with the Canadian division of Habitat for Humanity, and has been involved with World Vision.

In 2003, fifty of Mag's "Tool Girl" newspaper columns were compiled and put together to form the book, How Hard Can It Be, which is now available in Canadian and US bookstores. She currently has a blog up at www.toolgirl.com

Mag's other talents include singing and dancing.