Marcus Lorbeer (played by Pete Postlethwaite) wears a baseball cap that has a yellow equal sign (=) inside a blue square. This is the logo of Human Rights Campaign, a non-profit organization that lobbies for equal rights based upon sexual orientation and gender identity. It is the largest gay, lesbian, bisexual, and transgender advocacy organization in the United States.
Director Fernando Meirelles lobbied to have the movie shot in Kenya (where the story is supposed to take place) instead of in South Africa (where most of the film industry is located).
Ralph Fiennes held and operated the camera for Justin's point-of-view shots in the film.
After filming, the Constant Gardener Trust was set-up to help the inhabitants of the slums near Nairobi where the crew had been filming.
The scene where Tessa (Rachel Weisz) walks through the slum, numerous children ask her "How are you?" and she responds "I'm fine, how are you?" was unscripted. The children are actual children who live in Kibera and not extras.
The novel was originally banned in Kenya because it depicts corrupt Kenyan officials.
Cameo: [Jeffrey Caine] the writer appears as the The Liberal club's porter.
The character Tessa Quayle was based on famous social activist and charity worker Yvette Pierpaoli, who was killed in 1999 with two other social workers when their truck crashed in Albania. The book was written in her memory.
Swedish actress Pernilla August originally participated in the film, playing an employee at the Canadian company that was responsible for the drug research. Her character gave Justin Quayle information that led him to Dr. Lorbeer. Moments after doing this, she is killed in a mysterious hit-and-run car accident. The scene was deleted in the final cut but appears on as a feature on the DVD.
Justin's car's license number is 22CD 20K. The letters CD denote that the car belongs to a diplomat.
"Huruma", the play which Tessa Quayle watches in the market place, was directed by Nick Reding who played Crick in the film. It was performed by the Kizingo Arts Troupe.
Producer Simon Channing Williams bought the rights of the book in advance before its release in 2001 with the intention of bringing it to screen. In order to get John le Carré's permission to do so, he wrote a letter to Le Carre's attorney Michael Rudell informing him of the intention and flew to New York on the same day. This is the second time that Le Carre has worked on the screenplay of a film; the first was The Tailor of Panama (2001). To ensure total accuracy, Nairobi-based molecular biologist Dr. Bonnie Dunbar was brought in as the film's consultant.
To prepare for the film, Fernando Meirelles studied Brian Woods' and Michael Simkin's BBC documentary Dying for Drugs.
The filmmakers installed water tanks, a new bridge and a classroom in Kibera, the slum in which the film was shot. They also built a secondary school in the desert of northern Kenya where the final scenes were photographed.
Danish actress Iben Hjejle was originally cast as the German woman Birgit and was signed on. When the film's German financiers discovered that a Dane had been cast as a German, they made sure a German actress, Anneke Kim Sarnau, was cast instead.