The party was founded by followers of President Getúlio Vargas on May 15, 1945, during the final days of his Estado Novo.

"[2] PTB's support came from the trade unions controlled by the Ministry of Labour, and its trump card was the prestige of Getúlio Vargas, its honorary chairman, which introduced social and labor legislation in the country.

Vargas committed suicide in 1954, and his heir João Goulart became the central figure in the party along with the populist Leonel Brizola.

Since the party was a close ally of PSD, also founded by supporters of the late Vargas, it remained in power when Juscelino Kubitschek was elected president in 1955.

A new PTB, this time a centre-right party, was established by Ivete Vargas, Getúlio's niece, in 1980, with the end of the artificial two-party system imposed by the military regime.