Monroy joined the LDS Church in 1913. Shortly after this, Rey L. Pratt and the other missionaries of American citizenship were forced to leave because of the Mexican Revolution. Monroy was made a branch president by President Pratt.
Monroy was taken prisoner by the Liberation Army of the South (Zapatistas) in 1915. When asked to show his weapons, he held up the Bible and Book of Mormon and said "These are the only weapons I carry".