Hart was born in Halifax, Nova Scotia. Her father was a Court of Appeal judge. She graduated from the law school at the University of Toronto in 1973 and worked for law firms Weir and Foulds, Morris/Rose/Ledgett and Lerners in Toronto. At the time of entering public life in 1986, Hart was known as one of Canada's experts in transportation law.
Following the 1990 election, Hart continued to practice commercial and regulatory law and became accredited as a mediator and facilitator. In 1994 she was tapped to lead the Ontario Supreme Court's Alternative Dispute ResolutionPilot Project, which successfully provided an alternative to trial-based civil litigation, resolving more than half of the cases sent to it, before examinations for discovery. Hart joined KPMG as a partner in 1996, and in May 1997, she became president of KPMG Conflict Solutions Inc., a company specializing in conflict management services. In 1998 Hart founded Accord/hart & associates inc., a firm offering a comprehensive conflict management services across Canada, and she continues as its president resolving business and governance conflicts. Throughout her career, Hart has been an author and a teacher. Published works include "Bypass Court: A Dispute Resolution Handbook" with Genevieve Chornenki and "Freight Claims in Plain English", with Bill Augello. She has taught transportation, regulatory, environmental, ADR, and governance subjects in the Bar Admission Course, for the Law Society, the Ontario Bar Association, and continues to teach new judges how to mediate through the National Judicial Institute. Hart has actively served as a Director and Governor of a range of not-for-profit organizations for more than 30 years. Her long-standing interest in best governance practices led her to enroll and graduate from the University of Toronto Rotman School of Management's Director's Education Program, becoming an accredited Corporate Director in June, 2005. She is currently a member of the boards of the Centre for Addiction and Mental Health and the General Insurance OmbudService. Previous Board experience includes the Greater Toronto Airports Authority, Sheridan College, Roots of Empathy, Goodwill Toronto, Kingsway College School, Canadian Stage Company, Canadian Psychiatric Research Foundation, CNIB Library, Leaside Arthritis Society, and the Ontario Bar Association. From 2011 to 2016, Hart was a Board Member of Goodwill Toronto, until she abruptly resigned along with the rest of the Board.