Duhamel helped organize a rally in support of Louis Riel held in Montreal in 1885 and was one of the principal organizers for the Parti national in the Montreal region.
He ran unsuccessfully for a seat in the Quebec assembly in 1886.
He was elected later that year in a by-election held following the death of Alexis-Louis Demers.
He served in the provincial cabinet as solicitor general from 1887 to 1888 and as commissioner of crown lands from 1888 to 1891.
Duhamel was defeated when he ran for reelection in 1892.