[2] Born in Meaford, Canada West (now Ontario) to a Congregationalist minister, Duff received a Bachelor of Arts in mathematics and metaphysics from the University of Toronto in 1887.

[5] Duff was the first and only Puisne Justice of the Supreme Court of Canada to be appointed to the Imperial Privy Council.

He was made a Knight Grand Cross of the Order of St. Michael and St. George the following year[7] as a result of Prime Minister Richard Bennett's temporary suspension of the Nickle Resolution.

[citation needed] When Governor General Lord Tweedsmuir died in office on February 11, 1940, Chief Justice Duff became the Administrator of the Government for the second time.

[3] He held the office for nearly four months, until King George VI appointed Alexander Cambridge, 1st Earl of Athlone as Governor General on June 21, 1940.

[6] In 1942, Duff served as the sole member of a Royal Commission constituted to examine the Liberal government's conduct in relation to the defence of Hong Kong.

[10] Duff has been called a "master of trenchant and incisive English," who "wrote his opinions in a style which bears comparison with Holmes or Birkenhead.

"[13] Other writers have taken a less favourable view, instead arguing that Duff's reputation is largely unearned; his biographer concluded that he was not an original thinker, but essentially a "talented student and exponent of the law rather than a creator of it.

[15] As well, Lionel Schipper noted that, in reviewing Duff's judgments, it was: apparent that he has given certain factors very little consideration in formulating his decisions.