The Chilean bishop Manuel Larraín is one of the most relevant figures of the Latin American Catholic Church of the 20th century. His figure is reflected in various actions, some of which maintain their impact until today. Among the most notable actions are his intervention in favor of the freedom of Catholics to choose which political party to belong to, his essential participation in the creation of the Latin American Episcopal Council (CELAM), his episcopal role in the evolution of unionism and the delivery of Church lands to express the need for agrarian reform. This article addresses the development of his position regarding Catholic unionism in Chile. On this occasion, his epistolary, currently being edited, is used as a main source. These letters bring light from intimate reflection, at the same time, which reveal to us the evolution of its position, which ranges from the recognition of the value of the phenomenon, through the justification of Catholic unions, to the point of recognizing that the circumstances make preferable the action of Catholics within the unions to which they are affiliated.