Daniels was born in Salisbury, Wiltshire, England, the son of a plastics company executive. He studied law for two years at university and then dropped out to participate in amateur dramatics and attend Rose Bruford college. After leaving school in 1974, Daniels worked on BBC Radio and for the National Theatre of Great Britain at The Young Vic. Whilst working in the theatre, he was invited to meet director George Lucas who was casting for Star Wars. Daniels at first turned down the interview but was persuaded by his agent to meet Lucas.
Never a science fiction fan, Daniels has said that before his role in Star Wars the only science fiction film he had ever seen in a theatre was 2001: A Space Odyssey in 1968; he was so displeased with the film that he walked out after 10 minutes and demanded his money back. However, in a 2011 interview he said that he had watched it for longer than 10 minutes, and having since watched it in full, now regards it as a masterpiece. In the same interview, he said he enjoyed post-apocalyptic films such as Mad Max.
He speaks fluent French.
Daniels has played C-3PO in all of the Star Wars feature films from the original installment in the series, as both the body and voice of the golden robot. Kenny Baker, who played R2-D2 in the series until his death in 2016, revealed that he and Daniels did not get along.
In Star Wars Episode I: The Phantom Menace, he wore a blue Spandex costume so that during editing of the movie his body could be turned into many different wires and circuits. Daniels has reprised the role for various promotional work such as hosting The Making of Star Wars, Star Wars Connections and The Science of Star Wars; for appearances on The Muppet Show, Sesame Street and an anti-smoking public service announcement; the Star Wars Holiday Special; in advertising for Star Wars licensed products such as Kenner toys; and even a breakfast cereal based on the character.
Daniels voiced C-3PO in the Star Wars radio serial based on the original trilogy. He is the only cast member of the original Star Wars trilogy to voice his character in all three parts of NPR's dramatisations of the trilogy. He voiced C-3PO for four animated series: Droids, Star Wars: Clone Wars, Star Wars: The Clone Wars, and Star Wars Rebels. Other C-3PO voicework by Daniels includes: the Christmas-themed Christmas in the Stars album; the multiple Walt Disney theme park attractions, Star Tours and Star Tours: The Adventures Continue; the fan film/show Raiders of the Lost Jedi Temple of Doom: A Fan Film of Epic Proportions and the Star Tours shutdown ceremony as a part of the Disney's Hollywood Studios' "Last Tour to Endor" event at Star Wars Celebration V in Orlando, Florida. He also provided the narration and all character voices for the audio books Dark Force Rising and The Last Command.
Daniels contributed the foreword to the collected scripts of the Return of the Jedi radio drama, as their author Brian Daley died just as the episodes were being recorded. Daniels' other Star Wars-related writings include the Wonder Column for Star Wars Insider magazine and a comic book adventure for C-3PO and R2-D2 entitled The Protocol Offensive, published by Dark Horse Comics.
Daniels controlled the puppet for 2002's Star Wars: Episode II: Attack of the Clones, but all these scenes were cut, with the droid's first appearance in the film being Daniels in costume. In this film and 2005's Star Wars: Episode III: Revenge of the Sith, he also performed the vocal tracks for scenes that featured a computer generated C-3PO. Daniels is the only actor to act in the original seven films, the 2008 Clone Wars film, and the related television series.
Daniels hosted the Star Wars: In Concert North American tour.
Daniels also makes cameo appearances as a humanoid in two scenes of the feature films. His character, Lieutenant Dannl Faytonni, is named as a tribute to his own name, albeit in modified form. The character appears in the Outlander nightclub scene early in Star Wars: Episode II – Attack of the Clones as a man in blue uniform who can be seen in a cutaway reaction shot after Obi-Wan disarms the bounty hunter Zam Wesell. Faytonni can also be seen at the Galaxies Opera House in Star Wars: Episode III – Revenge of the Sith.
Daniels reprised his role as C-3PO in The Lego Movie when his character made a cameo appearance along with other crew members of the Millennium Falcon.
Daniels reprised his role as C-3PO in the seventh Star Wars film, Star Wars: The Force Awakens, which began filming in May 2014 and was released in December 2015. J.J. Abrams, the director for The Force Awakens, told Daniels that he was only going to be the voice of C-3PO in the film. However, Abrams changed his mind and decided Daniels would wear the suit in the film as well. Abrams made a new C-3PO suit for Daniels to wear during filming using 3D printing that allows Daniels a great deal more mobility and comfort than the original suit. Daniels is also signed to appear as C-3PO in the two sequels following The Force Awakens; they will be released in 2017 and 2019, respectively.
Daniels reprised his role as C-3PO in a surprise cameo for Rogue One: A Star Wars Story in 2016. It is the first stand-alone film in the Star Wars Anthology series.
In March 2017, ANA Airlines began domestic service of a plane styled after C3PO. Daniels was there to personally sign the plane.
Daniels was the voice of Legolas in the Ralph Bakshi animated adaptation of The Lord of the Rings (1978). He has appeared intermittently on British television in various dramas, notably in a recurring role in Prime Suspect starring Helen Mirren. He also played the priest in the British spoof horror film I Bought a Vampire Motorcycle (1990).
Daniels has appeared at Disney's Hollywood Studios in Orlando, Florida, for the Star Wars Weekends as he gave his "inside the saga" story.
Daniels is an adjunct professor at Carnegie Mellon University's Entertainment Technology Center.