He entered the Dominican Order as a teenager, and after his religious profession, pursued his studies at Valladolid and at the Monastery of San Pablo in Córdoba.

[2] His superiors sent Loayza to the missions of New Spain in 1529, where he worked in Cartagena serving both the Spanish colonists and the native Americans of the city.

In recognition of the reputation he had gained in this, he was appointed the first Bishop of Cartagena on December 5, 1537 by Emperor Charles V, which was approved by Pope Paul III.

[5] As the head of an ecclesiastical province, Loayza was vigorous in his efforts at establishing the mission of the Catholic Church in the New World, continuing to show the spirit of concern for the welfare of the indigenous population he had demonstrated in Cartagena.

In line with this, he requested that the pope issue a decree recognizing the humanity of the native peoples of the Americas and clarifying their proper treatment by the Spanish Empire.