Barry Fitzgerald was nominated by the Academy for both Best Actor and Best Supporting Actor awards for the same performance, the only time this has ever happened. He won the Oscar in the supporting category but lost in the lead category to co-star Bing Crosby (This is no longer possible under Academy guidelines.) Due to wartime metal shortages, Fitzgerald received a plaster Oscar (instead of a gold one) for his performance. A few weeks after he won, he broke the head off his plaster Oscar while practicing his golf swing.
Singer Andy Williams debuted as one of the singing boys surrounding Bing Crosby during the song "Swinging On A Star". Williams and his three other brothers were performing as the Williams Brothers and were all cast in the scene.
When Father O'Malley is talking to Jenny while she is getting ready to perform, the conductor can be seen taking out his cigarette case and opening it twice, in two adjacent shots.
Father Chuck O'Malley: Hail, Alma Mater, thy time-honored halls shall echo with our praise till we die; and round our hearts are the ivy-covered walls of East St. Louis High.