Margaret O’Sullivan exclusively practises estate planning, estate litigation, advising executors, trustees and beneficiaries, and administration of trusts and estates. Prior to establishing an independent trusts and estates boutique firm, she was a partner at Stikeman Elliott, where she directed its trusts and estates practice. She is a past deputy chair and member of the board of directors and council for the STEP Worldwide; past chair of the professional standards committee of STEP Worldwide; past member of the management and finance committee; past deputy chair of STEP (Canada); past chair of the editorial board for STEP Inside; past chair of the Trusts and Estates Law section, Ontario Bar Association; elected fellow, ACTEC, 1995; and academician of The International Academy of Estate and Trust Law. She received the 2014 STEP Founder’s Award for Outstanding Achievement and the Ontario Bar Association’s 2013 Award of Excellence in Trusts and Estates Law. 

She has written two textbooks for the Trust Institute of the Institute of Canadian Bankers: Engineering of a Trust and Trust and Estate Management. She is also author of the Canada chapter of International Succession Laws (Tottel, 2009) and contributing author to Widdifield on Executors and Trustees (Carswell, 2002), Key Developments in Estates and Trusts Law in Ontario (Canada Law Book, 2008) and to The International Comparative Legal Guide to: Private Client 2018 (Global Legal Group 2018). She was called to the Ontario Bar in 1983.