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 Society of Trust and Estate Practitioners (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 member of council, Ontario Bar Association (1993–1998). 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 2015 (Global Legal Group 2014). She was called to the Ontario Bar in 1983.