The former Catholic Bishop of Botucatu,[3] he was excommunicated by Pope Pius XII, ultimately for schism, but in culmination of several doctrinal and canonical issues (such as his views on clerical celibacy).

[5] He completed his primary studies at the Salesian College Santa Rosa, in Niterói, and at age nine, he received his first communion in the cathedral of Uberaba from the hands of his uncle, Dom Eduardo Duarte da Silva (now a bishop), on July 24, 1897.

Duarte Costa consistently maintained his left-wing allegiance, calling for the establishment of a "Christian communism" in contrast to "Roman [Catholic] Church Fascism".

[9] As long as he enjoyed the protection of Cardinal Dom Sebastiao Leme da Silveira Cintra, Duarte Costa's political activism proceeded without much trouble.

In addition, he announced plans to set up his own Brazilian Catholic Apostolic Church, in which priests would be permitted to marry (and hold regular jobs in the lay world), personal confessions and the praying of rosaries would be abolished and bishops would be elected by popular vote.

He immediately titled himself "Archbishop of Rio de Janeiro" and told the press that he hoped soon to ordain ten married lawyers and professional men as priests in his new church.

[11] After establishing the Igreja Católica Apostólica Brasileira (ICAB), Duarte Costa continued to use the same vestments, insignia, and rites as he had in the Roman Catholic Church.

[15] In the years immediately after founding the church, Duarte Costa consecrated four bishops, Salomão Barbosa Ferraz (August 15, 1945), Jorge Alves de Souza and Antidio Jose Vargas (both in 1946) and Luis Fernando Castillo Mendez (May 3, 1948).