Nichols was born in Robbins, Illinois, near Chicago, the daughter of Lishia (née Parks) and Samuel Earl Nichols, a factory worker who was both the town mayor of Robbins and its chief magistrate. Later, the family moved into an elegant apartment in Chicago after white residents fled because a single black family moved in.
She studied in Chicago as well as New York and Los Angeles. While still in Chicago, she performed at the "Blue Angel," and in New York, Nichols appeared at that city's "Blue Angel" and Playboy Club as a dancer and singer. She also appeared in the role of Carmen for a Chicago stock company production of Carmen Jones and performed in a New York production of Porgy and Bess. Between acting and singing engagements, Nichols did occasional modeling work.
She posed in a 1960 catalog for Hollywood fetish clothing seller Fine Craft, Inc. She posed nude for a layout in the December 1960 issue of the men's magazine Escapade and in January 1967 was featured on the cover of Ebony magazine.
Nichols toured the United States, Canada and Europe as a singer with the Duke Ellington and Lionel Hampton bands. On the West Coast, she appeared in The Roar of the Greasepaint—the Smell of the Crowd, For My People, and garnered high praise for her performance in the James Baldwin play, Blues for Mister Charlie. Prior to being cast as Lt. Uhura in Star Trek, Nichols was a guest actress on television producer Gene Roddenberry's first series, The Lieutenant.
It was in Star Trek that Nichols gained popular recognition by being one of the first black women featured in a major television series not playing a servant; her prominent supporting role as a female black bridge officer was unprecedented. During the first year of the series, Nichols was tempted to leave the show, as she felt her role lacked significance; however, a conversation with Dr. Martin Luther King, Jr. changed her mind. Though specifics of the conversation vary, in generalities she has reported that Dr. King personally encouraged her to stay on the show, telling her that he was a big fan of the series and told her she "could not give up" since she was playing a vital role model for black children and young women across the country. It is also often reported that Dr. King added that "Once that door is opened by someone, no one else can close it again."
Former NASA astronaut Mae Jemison has cited Nichols's role of Lt. Uhura as her inspiration for wanting to become an astronaut and Whoopi Goldberg has also spoken of Nichols's influence. Goldberg herself eventually landed a recurring role in Star Trek: The Next Generation as Guinan, while Jemison appeared in an episode of the series.
In her role as Lt. Uhura, Nichols famously kissed white actor William Shatner as Captain James T. Kirk in the 1968 Star Trek episode "Plato's Stepchildren". This is often referred to as the first interracial kiss on US television, however that milestone actually took place when Sammy Davis, Jr. and Nancy Sinatra kissed briefly on the variety program Movin' With Nancy in December 1967. It wasn't even the first interracial kiss on Star Trek, as Shatner had kissed an alien played by Vietnamese-French actress France Nuyen in the episode "Elaan of Troyius", which was screened earlier that season.
Nevertheless, the scene provoked protest and was seen as groundbreaking, even though the kiss was portrayed as having been forced by alien telekinesis. Despite a smattering of protest, the majority of the feedback of the incident was positive. In her 1994 autobiography, Beyond Uhura, Star Trek and Other Memories page 197, Nichols cites a letter from one white Southerner who wrote: "I am totally opposed to the mixing of the races. However, any time a red-blooded American boy like Captain Kirk gets a beautiful dame in his arms that looks like Uhura, he ain't gonna fight it." During the Comedy Central roast of Shatner on August 20, 2006, she referred to the incident and said, "Let's make TV history again ... and you can kiss my black ass!"
Despite the cancellation of the series in 1969, Star Trek lived on in other ways, and continued to play a part in Nichols's life. She again provided the voice of Uhura in Star Trek: The Animated Series; in one episode, "The Lorelei Signal", Uhura assumes command of the Enterprise. Nichols noted in her autobiography her frustration over this never occurring in the original series. Also, Nichols has costarred in six Star Trek films, her last being Star Trek VI: The Undiscovered Country.
After the cancellation of Star Trek, Nichols volunteered her time in a special project with NASA to recruit minority and female personnel for the space agency, which proved to be a success. Those recruited include Dr. Mae Jemison, the first American female astronaut and United States Air Force Col. Guion Bluford, the first African-American astronaut, as well as Dr. Judith Resnik and Dr. Ronald McNair, who both flew successful missions during the space shuttle program before their deaths in the Space Shuttle Challenger disaster on January 28, 1986.
An enthusiastic advocate of space exploration, Nichols has served since the mid-1980s on the Board of Governors of the National Space Society, a nonprofit, educational space advocacy organization founded by Dr. Wernher von Braun.
Always interested in space travel, Nichols flew aboard NASA's C-141 Astronomy Observatory, which analyzed the atmospheres of Mars and Saturn on an eight-hour, high-altitude mission. She was also a special guest at the Jet Propulsion Laboratory in Pasadena, California on July 17, 1976 to view the Viking 1 soft landing on Mars. Along with the other cast members from the original Star Trek series, she attended the christening of the first space shuttle, Enterprise, at the North American Rockwell assembly facility in Palmdale, California.
In 1994, she published her autobiography Beyond Uhura: Star Trek and Other Memories. In it, Nichols claimed that the role of Peggy Fair from the television show Mannix was offered to her during the final season of Star Trek but producer Gene Roddenberry refused to release her from her contract. Between the end of the original series and the Star Trek animated show and feature films, Nichols starred in minor roles in film and TV. She portrayed a foul-mouthed madam in Truck Turner (1974) opposite Isaac Hayes.
She appeared in animated form as one of Al Gore's Vice Presidential Action Rangers in the "Anthology of Interest I" episode of Futurama, and provided the voice of her own head in a jar in the episode "Where No Fan Has Gone Before". She voiced the recurring role of Diane Maza in the animated series Gargoyles and played the role of Thoth-Kopeira in an episode of Batman: The Animated Series. In 2004, Nichols provided the voice for herself in the Simpsons episode "Simple Simpson".
In 2006, Nichols appeared as the title character in the film Lady Magdalene's, the madam of a legal Nevada brothel in tax default. She also served as executive producer, choreographer, and sang three songs in the film, two of which she composed. She has twice been nominated for the Sarah Siddons Award as best actress and is an accomplished dancer and singer. Her first Siddons nomination was for her portrayal of Hazel Sharp in Kicks and Co. and the second for her performance in The Blacks.
She was cast in a recurring role on the second season of the NBC drama Heroes. Her first appearance was on the episode "Kindred" which aired on October 8, 2007. Nichols portrayed Nana Dawson, the matriarch of a New Orleans family financially and personally devastated by Hurricane Katrina. She cares for her orphaned grandchildren and her great-nephew, series regular Micah Sanders.
In 2008, she starred in the film The Torturer, playing the role of a psychiatrist.
In 2009 she joined the cast of The Cabonauts, a sci-fi musical comedy that debuted on the internet. Playing CJ, the CEO of the Cabonauts Inc, Nichelle is also featured singing and dancing.
Nichols has released two music albums. Down to Earth is a collection of standards released in 1967, during the original run of Star Trek. Out of This World is more rock oriented and is themed around Star Trek and space exploration.
Nichols' brother Thomas was a member of the Heaven's Gate cult; he died on March 26, 1997 in their mass suicide. A member for 11 years, he left an exit video saying "I'm the happiest person in the world."
Nichols' son is actor Kyle Johnson, who played the lead in Gordon Parks's The Learning Tree. Kyle is her son from her marriage to Foster Johnson in 1951, which was the same year she divorced him. She married again in 1968, but that marriage also was short-lived and ended in divorce.
In her autobiography, Nichols stated that she was involved in an extramarital affair with Star Trek creator Gene Roddenberry for several years in the 1960s. When Roddenberry's health was fading, Nichols co-wrote a song for him, titled Gene, that she performed at his funeral.
She is an honorary member of Alpha Kappa Alpha Sorority. Robert A. Heinlein in part dedicated his 1982 novel Friday to her. She now lives in Woodland Hills, California.