At age 16, Galvão gave up a promising future and his family's social influence, becoming a novice at the St. Bonaventure Friary in Vila de Macacu, Rio de Janeiro. There, he adopted the religious name of Anthony of Saint Ann, in honor of his family's devotion to Saint Ann. During his novitiate year, he was known for his piety, zeal and exemplary virtues. Galvão made his profession of solemn vows on 16 April 1761, taking the additional vow to defend the Blessed Virgin Mary's title of the "Immaculate Conception", which was still a controversial doctrine at that time.