Based on the book 'Greek Fire' by Nicolas Gage, the film will focus specifically on the singer's tempestuous love affair with business tycoon Aristotle Onassis. Mendes said that she was unable to turn down the project because 'Gosford Park' writer Julian Fellowes penned the film's script with her directly in mind.
In an interview with 'The Independent', Mendes said: "Julian Fellowes wrote a script for me based on the relationship between Maria Callas and Aristotle Onassis. "And as Julian Fellowes wrote it for me I couldn't say no to it."Since reading 'Greek Fire', Mendes admitted that she has become obsessed with the book and Callas's life. Mendes's next film 'Last Night' is due out on 3 June.