McGarrigle was born and grew up in Montreal, Quebec, with her sisters Kate and Anna.
[6] She served as her sisters' music manager for a time,[7] and also managed producers Pierre Marchand (Sarah McLachlan) and Robbi Finkel (Cirque du Soleil) and the group Three O'Clock Train.
[11] McGarrigle was a member of the Society of Composers, Authors and Music Publishers of Canada (SOCAN) and served on its board of directors from 1990 to 2000.
In 2013, she was part of a SOCAN representative group for a streamed panel, "Can the Music Industry be Saved?
"[13] With her sister Anna, she co-authored Mountain City Girls, a family memoir published in 2015 by Random House Canada.