Joseph La Rocque became Titular Bishop of Cydonia, and he later succeeded Jean-Charles Prince as Bishop of Saint Hyacinthe.
In 1860, he was transferred to succeed Prince as Bishop of Saint-Hyacinthe|Saint-Hyacinthe. When Prince was named Bishop of the Diocese of Saint-Hyacinthe, La Rocque was appointed Titular Bishop of Cydonia and Prince's successor as Coadjutor Bishop of Montreal. In 1852, La Rocque accompanied Coadjutor Bishop Jean-Charles Prince to Rome as his secretary. 
