sopinka was involved with several high-profile cases, including acting on behalf of susan nelles when she sued the government of ontario and the toronto police for malicious prosecution after the withdrawal of charges against her for murdering babies at the hospital for sick children in toronto. an inquiry into her case exonerated her and she won damages from the government for her ordeal. in 1986 he represented the ukrainian canadian committee at the deschênes commission of inquiry on war criminals and argued against the deportation of suspected war criminals to their native lands, particularly the soviet union. he also served as counsel to the william parker inquiry that looked into the conduct of former cabinet minister sinclair stevens.