In the mid-1980s, Duncan served as a special assistant to Progressive Conservative Deputy Prime Minister Erik Nielsen.
Liberal leader at the time, Ken Taylor, was unsuccessful in winning his Mount Lorne riding.
In the 2000 general election Duncan led the Yukon Liberal Party to a majority government, defeating New Democratic incumbent Piers McDonald.
[7] The Yukon Liberals were reduced to only one seat after the election - Duncan's own riding of Porter Creek South.
[9] At the 2005 Yukon Liberal Party leadership convention, Duncan was defeated by Arthur Mitchell by a margin of 357 votes to 303.