John Alton Duncan (1932–2007) was a Manitoba lawyer and judge.
In December 1978, Mr. Duncan was appointed Queen's Counsel.
In 1991 he was appointed to the Court of Queen's Bench of Manitoba, to serve as a Family Division judge in Brandon.
In 1996, he was transferred to the Family Division in Winnipeg, where he continued to serve as a judge until his retirement in 2006.
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