Hawks's production that became His Girl Friday was originally intended to be a straightforward adaptation of The Front Page, with both the editor and reporter being male. But during auditions, a woman, Howard Hawks's secretary, read reporter Hildy Johnson's lines. Hawks liked the way the dialogue sounded coming from a woman, resulting in the script being rewritten to make Hildy female and the ex-wife of editor Walter Burns. Most of the original dialogue and all of the characters' names were left the same, with the exception of Hildy's fiancé, Bruce Baldwin. Harry Cohn of Columbia Pictures approved Hawks's idea for the film project. Ben Hecht was unavailable to do do the necessary script revisions so Hawks recruited Charles Lederer who had worked on the adaptation for The Front Page to work on the screenplay.:96 Additions were made in the beginning of the screenplay by Lederer to give the characters a convincing backstory so it was decided that Hildy and Walter would be divorced with Hildy's intentions of remarriage serving as Walter's motivation to win her back.:97
Hawks had great difficulty casting this film. While the choice of Cary Grant was almost instantaneous, the casting of Hildy was a more extended process. At first, Hawks wanted Carole Lombard, whom he had directed in the screwball comedy Twentieth Century, but the cost of hiring Lombard in her new status as a freelancer proved to be far too expensive, and Columbia could not afford her. Katharine Hepburn, Claudette Colbert, Margaret Sullavan, Ginger Rogers and Irene Dunne were offered the role, but turned it down, Dunne because she felt the part was too small and needed to be expanded. Jean Arthur was offered the part, and was suspended by the studio when she refused to take it. Joan Crawford was reportedly also considered.
Hawks then turned to Rosalind Russell. During filming, Russell noticed that Hawks treated her like an also-ran, so she confronted him: "You don't want me, do you? Well, you're stuck with me, so you might as well make the most of it."
The film had the working title of The Bigger They Are, and was in production from September 27 to November 21, 1939.
In her autobiography, Life Is A Banquet, Russell wrote that she thought her role did not have as many good lines as Grant's, so she hired her own writer to "punch up" her dialogue. With Hawks encouraging ad-libbing on the set, Russell was able to slip her writer's work into the movie. Only Grant was wise to this tactic and greeted her each morning saying, "What have you got today?"
The film is noted for its rapid-fire repartee, using overlapping dialogue to make conversations sound more realistic, with one character speaking before another finishes. Although overlapping dialog is specified and cued in the 1928 play script by Hecht and MacArthur, Hawks told Peter Bogdanovich:
I had noticed that when people talk, they talk over one another, especially people who talk fast or who are arguing or describing something. So we wrote the dialogue in a way that made the beginnings and ends of sentences unnecessary; they were there for overlapping.
To get the effect he wanted, as multi-track sound recording was not yet available at the time, Hawks had the sound mixer on the set turn the various overhead microphones on and off as required for the scene, as many as 35 times.
Grant's character describes Bellamy's character by saying "He looks like that fellow in the movies, you know...Ralph Bellamy!" According to Bellamy, the remark was ad libbed by Grant. Columbia studio head Harry Cohn thought it was too cheeky and ordered it removed, but Hawks insisted that it stay. Grant makes several other "inside" remarks in the film. When his character is arrested for a kidnapping, he describes the horrendous fate suffered by the last person who crossed him: Archie Leach (Grant's birth name). Another line that people think is an inside remark is when Earl Williams attempts to get out of the rolltop desk he's been hiding in, Grant says, "Get back in there, you Mock Turtle." The line is a "cleaned-up" version of a line from the stage version of The Front Page ("Get back in there, you God damned turtle!") and Grant also played "The Mock Turtle" in the 1933 film version of Alice in Wonderland.