Sir Lyman Poore Duff,, PC(UK) was a Canadian lawyer and judge who served as the eighth Chief Justice of Canada. He was the longest-serving justice of the Supreme Court of Canada.

The chief justice of Canada is the presiding judge of the nine-member Supreme Court of Canada, the highest judicial body in Canada. As such, the chief justice is the highest-ranking judge of the Canadian court system. The Supreme Court Act makes the chief justice, a Crown in Council appointment, meaning the Crown acting on the advice of the prime minister and minister of justice. The chief justice serves until they resign, turn 75 years old, die, or are removed from office for cause. By tradition, a new chief justice is chosen from among the court's incumbent puisne justices.