In 1965, Mim Scala of the Scala Browne Agency saw O’Donnell’s strip and acquired the film rights to the character. Scala had the idea of casting Barbara Steele as Modesty with Michael Caine as Willie and Sidney Gilliat directing, but he sold the rights to produce the film to Joseph Janni, who had Monica Vitti and Joseph Losey as his clients. Caine would ultimately star in Alfie, a role intended for his friend and former flatmate Terence Stamp, who wound up playing Willie.
Modesty Blaise was released at the height of two cinematic trends: The popularity of James Bond had spawned a number of similarly themed films. Some were intended as serious spy adventures, others as parodies or pastiches of Bond and his genre. Director Joseph Losey and the screenwriters chose to follow the latter approach, by making Modesty Blaise a campy, sometimes surrealistic comedy-adventure. Playwright Harold Pinter made uncredited contributions to the final script.
Joseph Losey found it difficult to work with Monica Vitti, as she would invariably be accompanied on the set by director Michelangelo Antonioni, in whose movies she had become famous. Antonioni would often whisper suggestions to her, and she would take direction from him rather than Losey. Eventually, Losey asked Antonioni, whom he greatly admired, to keep away from the studios during filming. Antonioni complied. Dirk Bogarde likewise disliked working with her, saying in a radio interview years later that she was the only one of his leading ladies whom he had actively disliked.
Modesty Blaise includes a metafictional element during one sequence where Blaise, while visiting a friend’s apartment, comes across several newspapers with the Modesty Blaise comic strip, which are shown in close-up; artist Jim Holdaway’s work is prominently shown, as is Peter O’Donnell’s name. Supporters of the film suggest this indicates that the film is not intended to take place in the same „universe“ as the comic strip.
Comparison to source material
O’Donnell’s original screenplay went through a large number of rewrites by other people, and he often later complained that the finished movie retained only one line of his original dialogue. O’Donnell states this in some of his introductions to reprints of his comic strip by Titan Books. As a result, although the basic plotline and characters are based on the comic strip, such as Willie killing a thug in an alley, many changes were made.
Some are cosmetic — Vitti appears as a blonde for most of the film, except for one sequence in which she actually dresses up like a real-life version of the comic strip character. Likewise, Stamp initially appears in a blond wig and subsequently reverts to his natural dark hair. Other changes are more profound. For example, as the film progresses, Willie and Modesty fall in love and decide to get married, proclaiming the same during a sudden musical production number that pops up during a lull in the action. This breaks a cardinal rule set out by O’Donnell when he created the characters: They would never have a romantic relationship; the writer stayed true to this edict right up to the end of the comic strip in 2001.
The character of Sheikh Abu Tahir fills the function of Lob, Modesty’s adoptee father and mentor, who gives her the name „Modesty Blaise“. The Sheikh is otherwise an original character with no equivalent character in the source material. Other original characters include Paul Hagen, Mrs. Fothergill, McWhirter, and Nicole.