"A Double Life" is about an actor playing Othello. In December of 1947, the year that "A Double Life' was released, Arturo Toscanini, at that time considered the greatest conductor in the world, led a two-part radio broadcast performance of Giuseppe Verdi's "Otello", an operatic version of the play, with Ramón Vinay singing the title role.
Paddy Chayefsky, who later became a highly successful author and playwright ("Marty"), can be seen as an uncredited photographer at the death scene. According to Shelley Winters, Chayefsky needed the money to go to New York and get married.
In movie, Anthony John stars in a Broadway production of "Othello" that plays more than 300 performances and runs over a year. In reality, no production of a William Shakespeare play has chalked up anywhere near that many performances on Broadway; at best, most are lucky to run several months, like Richard Burton's four-month stint in a 1964 production of "Hamlet", which undoubtedly owed much of its success to his then-notorious relationship with Elizabeth Taylor.
In the film, Ronald Colman plays a fictional actor who stars in the longest-running "Othello" in history. In real life, actor Paul Robeson, who had just become the first black actor to star in an otherwise white production of "Othello" on Broadway, had just completed the longest run of the play.
The "Othello" scenes were filmed separately and in the exact order in which they occur in Shakespeare's play, so as to give Ronald Colman the feeling that he was actually appearing in "Othello". Colman felt uneasy about performing Shakespeare, so director George Cukor and Shakespearean actor Walter Hampden, who acted as coach and advisor for these scenes, tried to make Colman as comfortable as possible in them.
The role of Anthony John was originally written for Laurence Olivier. Olivier was unavailable when the film finally went into production.