Désilets ran as a Parti Québécois candidate in the provincial district of Maskinongé in 1994 and won.
He succeeded Liberal incumbent Yvon Picotte who had just retired from politics.
In 2003, he lost re-election against Liberal candidate Francine Gaudet.
He attempted a political comeback in 2007, but finished third, behind winner Jean Damphousse from the Action Démocratique du Québec and Gaudet who was running for re-election.
Désilets courted controversy in 2016 through an illegal contribution to a colleague's campaign fund, for which he was fined C$6,000.