He played Tier II Junior "A" hockey for the Salmon Arm Silverbacks in 2004-05. Then he went on to a stellar career with the North Dakota Fighting Sioux from 2005 to 2009. The highlight was winning the Hobey Baker Award in 2007.
Undrafted by the NHL, Duncan signed a tryout contract with the Bridgeport Sound Tigers (a New York Islanders' farm team) right after the 2008-09 Sioux season ended. He played in the Tigers' last two games of the season.
Duncan signed on with the Red Bulls in May, 2009.