Bishop Moreno graduated from Fullerton Junior College and UCLA where, in 1953, he received a degree in business administration.
After graduation, instead of beginning a business career, he began preparation for the vocation of the priesthood, entering Our Lady Queen of Angels Seminary in San Fernando, California.
He completed his preparation and studies at St. John’s Seminary in Camarillo, California, and was ordained on April 25, 1961.
As a new priest, he continued his studies at the graduate division of the North American College in Rome and then returned to Los Angeles for his first parish assignment.
On December 20, 1976, Pope Paul VI named Moreno an auxiliary bishop of Los Angeles, and on February 17, 1977, he was consecrated by Cardinal Timothy Manning.