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 later met Tony Gilroy, realized that they were both on the same page two hours into the meeting, and agreed to star. Washington said that he regretted his decision after seeing the movie.
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. Gilroy explained that right from the beginning, when he first read the script, he could tell "Realm and Conquest" was going to be a key prop. In the movie, it's a metaphor for truth and justice. To create the details of the fictional novel, Thompson generated original visuals inspired by German Expressionistic images cut from wood blocks, and Tony Gilroy wrote the first two pages for three chapters of the book. They even designed a "Realm and Conquest" card game for a scene between Henry and Michael. Thompson said, "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. Michael Clayton's home is in Blooming Grove, NY. Gilroy graduated from Washingtonville High School in 1974. Clayton graduated from Washingtonville Central High School in 1977. 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.
Director Tony Gilroy has written the scripts for all the Bourne series with Matt Damon. He never directed a Bourne edition with Damon in it. The first time he wrote AND directed a Bourne edition was The Bourne Legacy (2012). Tony's brother John Gilroy edited this movie, and some of the Bourne editions. Tony's son, Sam Gilroy, plays the clerk who hands the documents to George Clooney in the copy shop.
When 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.
When Clooney is in Wilkinson's loft, looking through the copy of the book his son recommended, the artwork of the horse on the hill was added through CGI as it was recommended to be a reason for Clooney to pull over and walk up the hill in the very early shot with the horses. (According to the commentary track, the editor was pushing for three horses in the photo, as just one wouldn't be enough for viewers to get the reference.)
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 The Devil Wears Prada (2006). It was cut in two for use in process shots featuring Meryl Streep and Anne Hathaway. It was then welded back together and repainted to be blown up in this film. Shooting Cars (2006) featured the car's preparation.