[2] He then furthered his studies at the Western Institute of Technology and Higher Education (ITESO) in Guadalajara, Mexico, earning a Master of Arts in psychology, and at the Pontifical Gregorian University in Rome.

[5] Returning to the United States in 1990, Garcia-Siller was named as rector of the Holy Spirit Missionaries' houses of studies in Lynwood and Long Beach, California, and in Portland, Oregon.

[6] In 1999, Garcia-Siller was appointed rector of the Missionaries theologate in Oxnard, California, also serving pastoral roles in three parishes of the Archdiocese of Los Angeles.

[4] He received his episcopal consecration on March 19, 2003, at Holy Name Cathedral in Chicago from Cardinal Francis George, with Bishops Raymond E. Goedert and Ricardo Urquidi serving as co-consecrators.

In March 2024, Garcia-Siller banned the Mission of Divine Mercy (MDM), a Catholic retreat house in New Braunfels, Texas, and the priest who was running it.