Once a Sinner is a 1950 British drama film directed by Lewis Gilbert and starring Pat Kirkwood, Jack Watling and Joy Shelton.

Bank clerk John Ross falls for good-time girl Irene and ends his relationship with his fiancee Vera.

Irene leaves her lover Jimmy Smart, a crook who has been passing forged bank notes, and although at first she tries to discourage John, they are quickly married.

In contemporary reviews Kine Weekly wrote: "Pat Kirkwood not only looks and acts the part as the streamlined Irene, Jack Watling registers in the unrewarding role of John, and Sidney Tafler is the most promising of the supporting players. ...

''[6] Allmovie wrote: "The magnificent Thora Hird steals the show in Once a Sinner as the fickle Irene's slatternly mother.