Stickler was born in Neunkirchen, near Vienna, as the second of twelve children. He entered the Salesians of Don Bosco in a German novitiate, and made his profession on 15 August 1928. Thereafter, Stickler studied philosophy in Germany and then in Austria, Turin, and Rome. He studied canon law at the Pontifical Athenaeum of S. Apollinare (from where he received his doctorate) and the Pontifical Lateran University, and was ordained to the priesthood on 27 March 1937. (Stickler studied with Stephan Kuttner, who lived to see his first pupil in the history of canon law become a cardinal.)