From 1946 he taught at the University of Saskatchewan and then moved to Ontario the following year to practice law. In 1973, he was appointed to the Court of Appeal for Ontario and two years later was named Chief Justice of the High Court of Justice of Ontario. He became Chief Justice of Ontario in 1976. He was appointed to the Supreme Court of Canada in 1977 to replace Wilfred Judson.
Willard Estey retired from the Supreme Court of Canada in 1988.
Estey was appointed a trustee of the Stanley Cup in 1984 on the nomination of Red Dutton, succeeding Clarence Campbell. In 1985, he was appointed as Commissioner of Inquiry into the collapses of the Canadian Commercial Bank and the Northland Bank, both of which had been closed by the Canadian government that year. His report, Report of the Inquiry into the Collapse of the CCB and Northland Bank, was issued in 1986.[2]