Reverend Father Carlos Duarte Costa was awarded with title of Monsignor for his publication of a catechism for children. Soon afterwards, he was nominated Apostolic Protonatario and General Secretary of the Archdiocese of Rio de Janeiro, for His Eminence. Cardinal Sebastião Leme da Silveira Cintra who succeeded His Eminence Cardinal Joaquim Arcoverde de Albuquerque Cavalcanti, executing this function until May 24, 1923, when his was nominated as Vicar General of the Archdiocese of Rio de Janeiro. He was later consecrated sacred Diocesan Bishop of Botucatu in 1924 by his friend Most Reverend Dom. Sebastião Leme da Silveira Card. Cintra , Archbishop of Rio de Janeiro.
He was Bishop Emeritus of Botucatu and renamed in 1936 by Pope Pius XI as Titular Bishop of Maura as a form of punishment and acceptance of his resignation from the Roman Catholic Church.
Since the death of His Excellency Bishop Lacio in 1923, Botucatu remained a vacant diocese. For his work, for his dynamism and virtues, in the fulfilment of his duty in the Archdiocese of Rio de Janeiro.
His Holiness. Pope Pius XI (Most Reverend Ambrogio Cardinal Damiano Achille Ratti) nominated Monsignor Carlos Duarte Costa as the Diocesan Bishop of Botucatu on July 04, 1924.
Monsignor Duarte Costa’s Episcopal consecration took place at the Metropolitan Cathedral of Rio de Janeiro, on December 8, 1924.
Roman Catholic Diocesan Bishop Duarte Costa was consecrated by His Eminence the Most Reverend Sebastião Leme Cardinal da Silveira Cintra, assisted by Most Reverend Dom. Alberto José Gonçalves, His Excellency the Bishop of Ribeirão Preto, and the Most Reverend Dom. Benedito Paulo Alves de Souza, His Excellency the Bishop of Espírito Santo. Brazil. who laid hands upon him.