Prior to running for office, he was a Social Credit activist and managed a furniture store.
Guay ran as a candidate of the Ralliement créditiste in the 1970 provincial election and won, becoming the Member of the National Assembly for the district of Dorchester.
During his term of office, the party was plagued by internal divisions.
Eventually, the Samson faction re-joined the party and Yvon Dupuis was chosen as leader.
Nonetheless, Guay was defeated and finished third in the district of Beauce-Nord in 1973.