Coulter Osborne played basketball for the University of Western Ontario, graduating from there in 1955. He then entered Osgoode Hall Law School, earning his law degree in 1959, the same year he was Called to the Bar. He worked as a partner of the firm Lochead, Sills, Osborne, Madorin & Bean from 1959-70, and then formed his own firm as senior partner, Osborne, Millison, Boehler, serving with them from 1970-78. During his legal career, he was appointed to the Supreme Court of Ontario, High Court of Justice in 1978 and in 1999 was appointed Associate Chief Justice for Ontario.