Majel began taking acting classes as a child. She attended Shaker Heights High School, graduating in 1950 before going on to the University of Miami in Coral Gables, Florida, then had some stage roles and came to Hollywood. Her father, William Hudec, was a Cleveland police officer. He was killed in the line of duty in 1955 while Majel was touring with an off-Broadway road company. She was briefly seen in Will Success Spoil Rock Hunter? (1957) in an ad parody at the beginning of the film, and had roles in a few movies including Love in a Goldfish Bowl (1961), Sylvia (1965), A Guide for the Married Man (1967) and Track of Thunder (1967). She worked at the Desilu Studios on several TV shows, including Bonanza, The Untouchables, The Lucy Show, and The Lieutenant (produced by Gene Roddenberry). She received training in comedy from Lucille Ball. In 1960, she played Gwen Rutherford on Leave It to Beaver. In various roles, Barrett participated in every incarnation of the popular science fiction Star Trek franchise produced during her lifetime, including live-action and animated versions, television and cinema, and all of the time periods in which the various series have been set. She first appeared in Star Trek’s initial pilot, “The Cage” (1964), as the USS Enterprise’s unnamed first officer, “Number One”. Barrett was romantically involved with Roddenberry, whose marriage was on the verge of failing at the time, and the idea of having an otherwise unknown woman in a leading role just because she was the producer’s girlfriend is said to have infuriated NBC network executives who insisted that Roddenberry give the role to a man. William Shatner corroborated this in Star Trek Memories, and added that female viewers at test screenings hated the character as well. Shatner noted that women viewers felt she was “pushy” and “annoying” and also thought that “Number One shouldn’t be trying so hard to fit in with the men.” Barrett often joked that Roddenberry, given the choice between keeping Mr. Spock (whom the network also hated) or the woman character, “kept the Vulcan and married the woman, ’cause he didn’t think Leonard [Nimoy] would have it the other way around.”

Her role in subsequent episodes of Star Trek was altered to that of Nurse Christine Chapel, a frequently recurring character, known for her unrequited affection for the dispassionate Spock. Her first appearance as Chapel in film dailies prompted NBC executive Jerry Stanley to yodel “Well, well–look who’s back!”. In an early scene in Star Trek: The Motion Picture, viewers are informed that she has now become Doctor Chapel, a role which she reprised briefly in Star Trek IV: The Voyage Home. Barrett provided several voices for Star Trek: The Animated Series, including those of Nurse Chapel and a communications officer named M’Ress, an ailuroid officer who served alongside Uhura. She would return years later in Star Trek: The Next Generation, cast as the outrageously self-assertive, iconoclastic Betazoid ambassador Lwaxana Troi, who appeared as a recurring character in the series. Her character often vexed the captain of the Enterprise, Jean-Luc Picard, who spurned her amorous advances. Barrett later appeared as Ambassador Troi in several episodes of Star Trek: Deep Space Nine, where in stark contrast, she developed a strong relationship with Constable Odo. She provided the regular voice of the onboard computers of Federation starships for Star Trek: The Original Series, Star Trek: The Next Generation, Star Trek: Deep Space Nine, Star Trek: Voyager, and most of the Star Trek movies. She reprised her role as a shipboard computer’s voice in two episodes of the prequel series Star Trek: Enterprise, thus making her the only actor to have a role in all six televised Star Trek series. She also lent her voice to various computer games and software related to the franchise. The iconic association of her voice to interactions with computers led to Google’s Assistant project being initially codenamed Google Majel. Barrett had also made a point of attending a major Star Trek convention each year in an effort to inspire fans and keep the franchise alive.

Barrett is also one of six actors (the others being Jonathan Frakes, Kate Mulgrew, George Takei, Avery Brooks and Michael Dorn) to lend their voices to the CD-ROM Star Trek: Captain’s Chair, reprising her role as the voice of the ships’ computers. On December 9, 2008, less than 10 days before her death, Roddenberry Productions announced that she would be providing the voice of the ship’s computer once again, this time for the 2009 motion picture relaunch of Star Trek. Sean Rossall, a Roddenberry family spokesman, stated that she had already completed the voiceover work, approximately December 4, 2008. The film is dedicated to her as well as Gene. Barrett and her husband, Gene Roddenberry, were honored in 2002 by the Space Foundation with the Douglas S. Morrow Public Outreach Award for their work creating awareness of and enthusiasm for space. She appeared as Primus Dominic in Roddenberry’s 1973 post-apocalyptic TV drama pilot, Genesis II, as Dr. Bradley in his 1974 TV movie The Questor Tapes, and as Lilith the housekeeper in his 1977 TV drama pilot, Spectre. She also appeared in Michael Crichton’s 1973 sci-fi western, Westworld as Miss Carrie, a robot brothel madam, the 1977 Stanley Kramer thriller The Domino Principle, and the 1979 TV movie The Man in the Santa Claus Suit starring Fred Astaire. Her later film appearances included small roles in Teresa’s Tattoo (1994) and Mommy (1995). After Gene Roddenberry’s death, Barrett took material from his archives to bring two of his ideas into production. She was executive producer of Earth: Final Conflict (in which she also played the character Dr. Julianne Belman), and Andromeda. She also served as creative director for Gene Roddenberry’s Lost Universe, a comic book series based on another archival Roddenberry concept.

In a gesture of goodwill between the creators of the Star Trek franchise and of Babylon 5 (some of whose fans viewed them as rivals), she appeared in the Babylon 5 episode “Point of No Return”, as Lady Morella, the psychic widow of the Centauri emperor, a role which foreshadowed major plot elements in the series. Parodying her voice work as the computer for the Star Trek series, Barrett performed as a guest voice on Family Guy as the voice of Stewie Griffin’s ship’s computer in the episode “Emission Impossible”. Barrett-Roddenberry died on the morning of December 18, 2008, at her home in Bel Air, Los Angeles, California, as a result of leukemia. She was 76 years old. A public funeral was held on January 4, 2009, in Los Angeles. More than 250 people attended including Nichelle Nichols, George Takei, Walter Koenig, her on-screen daughter Marina Sirtis, Brent Spiner, Wil Wheaton and many Trekkies. After Gene Roddenberry died in 1991, his wife had commissioned Celestis Inc., a company that specializes in “memorial spaceflights”, to launch a part of his remains into space in 1997. On January 26, 2009, Celestis said that it would ship the remains of Gene Roddenberry and Majel Barrett-Roddenberry into space the following year, but the launch has been delayed. The couple’s cremated remains will be sealed into specially made capsules designed to withstand space travel. A rocket-launched spacecraft will carry the capsules, along with digitized tributes from fans. The spacecraft is currently planned to launch in 2016.