Born in Limerick, Cantwell was the first of fifteen children. At a time when Ireland had a priestly surplus, newly ordained priests were often sent to other dioceses around the world that needed priests. Cantwell was sent to San Francisco, where he organized the Newman Club on the University of California’s Berkeley campus. In 1904, he became secretary to San Francisco Archbishop Patrick Riordan, and in 1914 he was named Vicar General of the Archdiocese. In 1917, he was named Bishop of Monterey-Los Angeles. In 1922, the diocese was renamed Los Angeles-San Diego, before it was named the Archdiocese of Los Angeles in 1936.) As Archbishop of Los Angeles, Cantwell oversaw the erection of a major seminary, 16 hospitals and clinics, 205 parishes, 34 high schools, and 43 parochial schools. During his tenure the number of Catholics grew from 178,000 to 601,000. He also established the Catholic Motion Picture Actor’s Guild of America, which evolved into the Legion of Decency.