Drouin won a by-election in 1928 and became the Liberal Member of the Legislative Assembly of Quebec for the district of Québec-Est.

He joined the newly formed Action libérale nationale (ALN) in 1934 and was re-elected as a candidate of that party in the 1935 election.

After the ALN merged with the Conservative Party to form the Union Nationale, Drouin became Maurice Duplessis's campaign manager.

He and colleagues René Chaloult, Joseph-Ernest Grégoire, Philippe Hamel and Adolphe Marcoux left the Union Nationale.

He served as Minister of Municipal Affairs in Premier Adélard Godbout's Cabinet.