Burt Reynolds said of working with his co-star Dyan Cannon in his autobiography "My Life" (1994): "As Dyan and I walked down Broadway one afternoon a guy stopped us and asked for a picture. A camera dangled around his neck. 'Well, okay,' I said. Grinning broadly, he put his arm around Dyan and handed me the camera."
The cat in this film was called "Morris" and was well-known from the famous "9-Lives" cat food television commercials. The feline was also even billed in the movie's credits. Moreover, Morris had just recently won a PATSY Award for (as the acronym goes) Performing Animal Television Star of the Year (special award, commercials) for the previous 1972 year. Morris the Cat also appeared in another film noir detective film around the same time as Shamus (1973), that being in the same 1973 year's adaptation of Raymond Chandler's The Long Goodbye (1973) directed by Robert Altman.
There is a shot in the movie where Burt Reynolds grabs a tree branch during a chase scene, it breaks and he falls to the ground. That was not planned. The branch broke accidentally during filming and the footage looked so good, they kept it in the film. This particular stunt was performed by stuntman Hal Needham. He subsequently suffered a concussion when he hit the ground.
Due to the presence of star Burt Reynolds, an NYPD estimated three thousand onlookers, mainly women and teenagers, attended the first day of principal photography in Brooklyn, New York City.
The movie has a few notable references to Howard Hawks's filmed adaptation of Raymond Chandler's The Big Sleep (1946). The Shamus McCoy (Burt Reynolds) character is a tribute to Philip Marlowe (Humphrey Bogart) in this earlier film; McCoy's meeting in a cold study with E.J. Hume resembles Marlowe's meeting with General Sternwood in a hot greenhouse; and McCoy enters a bookstore in order to keep an eye on someone in a business across the street, seduces the shop-girl, who pulls the closed shade, and after an unseen tryst, offers the gazette, which is nearly identical to scene with Bogart and Dorothy Malone.