Entering politics in the mid-1950s, Franco first served as alderman and deputy mayor of Juiz de Fora, before getting elected as mayor (1967 to 1971 and again from 1973 to 1974). He resigned as mayor in 1974 and ran successfully for the Federal Senate, representing Minas Gerais. He soon became a senior figure in the Brazilian Democratic Movement (Movimento Democrático Brasileiro, MDB) the official opposition to the military regime that ruled Brazil from 1964 to 1985. He served as deputy leader in 1976 and 1977.