Denzel Washington turned down the title role, saying he was skeptical of working with a first-time director. George Clooney also originally turned it down for the same reason. Clooney upon meeting Gilroy, realized that they were both on the same page regarding the film two hours into their meeting, prompting Clooney to star.
Committed to a fully developed back story, director Tony Gilroy spent a good deal of time establishing the details of "Realm and Conquest" with production designer Kevin Thompson. The director explains that right from the beginning, when he first read the script, he could tell that "Realm and Conquest" was going to be a key prop. In the movie it's a metaphor for truth and justice. In creating the details of the fictional novel, Thompson generated original visuals inspired by German Expressionistic images cut from wood blocks, and Gilroy wrote the first two pages for three chapters of the book. They even went as far as designing a "Realm and Conquest" card game for a scene between Henry and Michael. Thompson offers, "This detail was important to Tony because, in his own life, novels and games similar to 'Realm and Conquest' allow him to connect with his son in a meaningful way."
Early on in the process of making this film, director Tony Gilroy secured Sydney Pollack as one of the producers. Gilroy said in an interview, regarding Pollack, "He read the script and wanted to direct it himself, and I told him I was saving it for me."
Tony Gilroy grew up in Orange County, New York, about 65 miles north of New York City. In the film, Michael Clayton graduated from Washingtonville Central High School in 1977. Gilroy graduated from Washingtonville High School in 1974. Clayton's home is in Blooming Grove, NY. The scene where Michael boards a private jet was filmed at Stewart International Airport in Newburgh, NY. The pivotal car accident was filmed at the Moodna Viaduct in Salisbury Mills, NY.
During a scene where Edens is wandering through Times Square, a U-North advertisement appears on a massive video screen. Beneath the screen on the side of a bus is another advertisement for a musical called Wicked. While Wicked is about the witches of Oz, its appearance in the same shot as the name of the company Edens was defending is appropriately coincidental given the plot of the movie.
George Clooney, Tilda Swinton, and Tom Wilkinson have all been in comic book movies. George Clooney played Bruce Wayne/Batman in Batman & Robin (1997), Tilda Swinton played the Ancient One in Doctor Strange (2016), and Tom Wilkinson played Carmine Falcone in Batman Begins (2005), making him and Clooney related to the same media.
The trivia items below may give away important plot points.
The Mercedes-Benz S-Class sedan that is blown up in this film was first used in filming of The Devil Wears Prada (2006). For the earlier film it was cut in two for use in process shots featuring Meryl Streep and Anne Hathaway. It was then welded back together and repainted in order to be blown up in Michael Clayton (2007). The car's preparation was featured on Shooting Cars (2006).