Rosalind Russell received an Academy Award nomination for her role as Lavinia in this movie. Apparently, she was so sure she was going to win that when the winner was about to be announced, she had risen from her seat to accept it... only to discover that Loretta Young had won for her performance in The Farmer's Daughter (1947).
The movie is one of three RKO-distributed movies that were edited heavily after their initial unsuccessful first runs. The others were The Devil and Daniel Webster (1941) and Joan of Arc (1948). All three have been restored to their full lengths (or, in the case of this movie, approximately its full length) on DVD.
Eugene O'Neill liked Writer, Producer, and Director Dudley Nichols' adaptation of "The Long Voyage Home" so much that he allowed him to film "Mourning Becomes Electra". O'Neill and The Theater Guild agreed to defer payment until the movie made a profit.
Although billed ninth in the credits, Sara Allgood appears in only one scene as Adam Brant's (Leo Genn) landlady in New York City, and she does not have a single line of dialogue. She is only seen climbing the stairs in one shot that is less than ten seconds long.
Writer, Producer, and Director Dudley Nichols disclaimed screenplay credit because he only abridged the play's text and moved some scenes outdoors. His first finished cut ran over four hours, but was edited down to two hours and fifty-four minutes for its roadshow premiere.