Carroll was ordained to the priesthood by Bishop Marius Besson in Fribourg for the Diocese of Pittsburgh on April 2, 1927.[2] Following his return to Pennsylvania in 1928, the diocese assigned Carroll as a curate at Sacred Heart Parish in Pittsburgh. In 1938, he was named assistant general-secretary of the National Catholic Welfare Council (NCWC) in Washington, D.C. The Vatican named Carroll as a papal chamberlain in 1942 and a domestic prelate in 1945. He served as general-secretary of NCWC from 1944 to 1957.