In an interview on Inside the Actors Studio (1994), Robert Downey, Jr. said that while preparing for the movie, he watched all of Charlie Chaplin's movies. When asked what how he felt about them, he said, "They scared the hell out of me."
During the scene when Chaplin is at work on Shoulder Arms (1918), he asks his cameraman Roland Totheroh how the light is. Totheroh (and the rest of the crew) replies "Better down at Barney's bar". This was the signal for production to end for the day, the "light", to which Chaplin was referring, was the light beer served at Barney Oldfield's bar, which was the favorite drink and hangout for the crew after filming.
While researching his role, Robert Downey, Jr. visited the Museum of the Moving Image in London and persuaded the staff to let him try on one of Charlie Chaplin's Little Tramp suits and boots. The latter fit him perfectly, and he found a cigar stub in one of the pockets, which he subsequently treasured.
Originally called "Charlie", as he was known among his friends, family, and fans. The makers of the Cliff Robertson movie Charly (1968) complained that the title would lead to confusion with their movie, so the film had to be renamed "Chaplin".
Kevin Kline was originally considered by Sir Richard Attenborough to play Charlie Chaplin. Kline originally turned down the role of Douglas Fairbanks, because his child had just been born. Attenborough agreed to delay the shooting of Kline's scenes for a month.
When Chaplin arrives in Hollywood (to join Mack Sennett), a film is being made. Chaplin joins in and improvises a complex scene. This is actually the final chase sequence from The Adventurer (1917). The location for the last shots of the opening sequence of the same film are used when Chaplin takes Oona Chaplin on a tour of his old haunts, just before they leave for Europe.
Geraldine Chaplin recalled that when she first saw Robert Downey, Jr. in full costume, she was so awestruck on how much he resembled her late father, that she needed a moment to collect her thoughts to even speak.
Sir Richard Attenborough turned down many film roles, because of obligations to the pictures he had directed. Due to the post-production and promotion of this film, he almost had to do so again when Steven Spielberg offered him the role of John Hammond in Jurassic Park (1993). However, unlike many other film directors, Spielberg offered to move his production schedule to accommodate Attenborough.
The film was originally to be distributed by Universal, but the studio wanted a bigger name in the starring role than Robert Downey, Jr., preferring Dustin Hoffman or Billy Crystal. When Sir Richard Attenborough refused to comply, the movie was put into turnaround, and a new producer had to be found. Mario Kassar agreed to take the reigns, but demanded that the film include the latter part of Chaplin's life in Switzerland. William Goldman was then brought in to write these new sequences.
Robert Downey, Jr. mentioned in a 2013 interview, that during his first audition, Sir Richard Attenborough held up a picture of Tom Cruise, and told Downey that he was also considering Cruise for the part. Downey said that he was unsure if Cruise was actually in contention for the role, or whether this was merely a motivational tactic by Attenborough.
Bryan Forbes' discarded script had a different beginning, and focused on some darker elements of Chaplin's life and personality. Although his script was not used, the WGA ruled that Forbes got writing credit, because much of the film's framework was derived from his script.
In real-life, Charlie Chaplin's eyes were reportedly very strikingly blue by those who knew him, but in the movie, Robert Downey, Jr.'s are hazel. (They look dark brown at first glance, but the brighter lighting of his face in "Restoration" reveals his eyes to be hazel with green highlights.)
To prepare for his role, Robert Downey, Jr. learned how to play the violin and tennis left-handed. He also had a personal coach in order to help him imitate Charlie Chaplin's posture and way of carrying himself.
Although Roland Totheroh is depicted in this film to have worked with Chaplin at Keystone in 1914, it was not until a year later that the two began their working relationship that was to last thirty-seven years, from 1915, until Chaplin was exiled from the United States in 1952.