- Although James Stewart is 6'4'', he refers to Harvey as being 6'3 1/2'' tall in the film and looks up at him during the entire film. That's because this is Harvey's height in the original play by Mary Chase. In a 1990 interview, Stewart said that he had decided that for the film, Harvey was going to be 6'8'', so that he could indeed look up at him.
- At the suggestion of James Stewart, the director changed many shots to make them wider so that "Harvey" would be in the frame.
- Josephine Hull first performed her role in the Broadway version of Harvey. Jesse White also appeared in the original Broadway production and a 1972 television version.
- The original Broadway production of "Harvey" by Mary Chase opened on November 1, 1944 at the 48th Street Theatre, ran for 1775 performances and won the Pulitzer Prize in Drama in 1945.
- Though James Stewart's character, Elwood P. Dowd, may certainly be referred to as an alcoholic, only at one time in the entire picture is he seen taking a drink.
- Prior to the release of Harvey, a press release reported that Francis the Talking Mule would have a cameo appearance in the movie. James Stewart, as Elwood P.Dowd, was to walk past Francis, and Francis was to "speak". Elwood would turn, in order to respond, but Francis would rebuke him, stating that he was talking to the big rabbit.
- Universal-International paid $750,000 for the film rights.
- First film project of Fess Parker.