Prior to his appointment, Justice Wilton-Siegel spent his legal career at Torys LLP, becoming a partner in 1982. His practice was concentrated in the area of corporate and securities law, principally in financing and mergers and acquisitions. During the period between 1988 and 1990, Justice Wilton-Siegel acted as the policy advisor to the Minister of Financial institutions for the Province of Ontario while on a sabbatical. Over the course of his career, he served on a number of boards of directors including Dayton Mining Corporation, the Doctor’s Hospital, and the Toronto Port Authority.

Justice Wilton-Siegel was called to the Bar of Ontario in 1977. He received his LLB from Dalhousie University in 1975 and his LLM from Harvard University in 1978. He was also previously educated at the University of Toronto as well as Oxford University, which he attended as a Rhodes Scholar between 1971 and 1974.