LeParmentier, born near Pittsburgh, Pennsylvania in the United States on July 16, 1946, grew up on a dairy farm. His father came from the isle of Guernsey and his mother from County Mayo in Ireland. LeParmentier lived in Hollywood, Florida during his teen years, and there his school drama-teacher suggested he become a professional actor. He attended a drama course at Wayne State University in Detroit, Michigan before moving to the United Kingdom in 1974.

After appearing in a Fringe theatre production that was broadcast by the BBC, LeParmentier was granted an Equity union membership card and toured with the Incubus Theatre Company. His first film role was as Lawyer Felix Hoffman in the 1974's Stardust and the following year he appeared in the film Rollerball. He also made numerous appearances on British television. His most prominent role was that of Admiral Motti, the arrogant, mocking Imperial officer who is choked by Darth Vader in Star Wars (1977), after Vader finds his "lack of faith disturbing". Mark Newbold, writing on the official Star Wars website, described the role as leaving "an indelible imprint on the Star Wars galaxy, helping to illustrate the fearsome powers of Lord Vader as well as the arrogance and malice of a bloated and over-confident Empire." LeParmentier had auditioned for the role of Han Solo, one of the film's main characters. The auditions for Star Wars were also used for Brian DePalma's Carrie and LeParmentier was cast as the high school principal in the latter. The film's production was delayed for nine months, so LeParmentier had to drop out of the role. He was offered a two-line role as a customs officer in Star Wars, but deemed the part too small. Star Wars' Writer and Director George Lucas cut the part, and the following month LeParmentier was cast as Motti. Additionally prior to gaining the role, LeParmentier was initially to portray a "Mos Eisley bureaucrat named Montross." However, before production began, the character was ultimately omitted from the film.

From 1981 to 1984, LeParmentier was married firstly to the British Actress Sarah Douglas, who is best known for playing the role of Ursa in Superman and Superman II. The two appeared in several films together, including Rollerball, The People That Time Forgot, and Superman II. He had three children with his second wife, Cheryl Le Parmentier: Rhiannon, Stephanie and Tyrone. He was staying with them at the time of his death.

LeParmentier lived in Bath, Somerset, England. He died suddenly on April 15, 2013, while visiting his family in Austin, Texas, United States, aged 66.