Arguably, Prowse is best known for playing the physical form of Darth Vader in the original Star Wars trilogy. He spoke the dialog during the filming of the movie, and didn't actually know he was Luke's father until he saw the movie in the theatres.

Though he was never going to be used as the voice of Darth Vader, he was originally told that he would be seen and heard at the end of Return of the Jedi when Vader's mask was removed. This did not end up happening as actor Sebastian Shaw was brought in instead.

However, Lucas claims he wanted a 'darker voice' (Lucas has stated that Darth Vader had to have a deep, reverberating voice) that Prowse could not provide and never intended to use Prowse's voice. In the 2004 documentary, Empire of Dreams, actress Carrie Fisher, who played Princess Leia Organa in the original trilogy films, quipped that they nicknamed Prowse "Darth Farmer" because of his un-intimidating West Country accent.

In the lightsabre battle scenes, Prowse's fencing coach Bob Anderson (who also taught the sword fighters in The Princess Bride and Lord Of The Rings) took his place as a stunt double.

Prowse continues to associate himself with his role in the Star Wars films and is involved in the convention circuit. Despite this, he has not been included in recent reunions of the original cast, such as those for the Empire of Dreams documentary and the 2005 Vanity Fair cover.

Within the United Kingdom, Prowse is also well-known as the Green Cross Code Man, a superhero invented to promote a British road safety campaign for children in 1975. As a result of his association with the campaign which ran between 1971 and 1990 he received the MBE in 2000.

He had a role as F. Alexander's bodyguard Julian in the 1971 film A Clockwork Orange, and as a circus strongman in 1972's Vampire Circus. He played the Minotaur in the 1972 Doctor Who serial The Time Monster. He also appeared in an episode of Space:1999, The Beta Cloud in 1976 right before he was cast as Darth Vader.

He had a small role as Hotblack Desiato's bodyguard in the 1981 BBC TV adaptation of The Hitchhiker's Guide to the Galaxy. He also appeared in the first series of The Tomorrow People on LWT and as a bodyguard in 'Callan'. He played Charles, the duke's wrestler, in the BBC Television Shakespeare production of As You Like It in 1978.

Prowse played Frankenstein's monster three times. He first appeared in Casino Royale. He then appeared in The Horror of Frankenstein in a more or less recognizable form. In Frankenstein and the Monster from Hell, he was heavily made up.