Campbell decided to use the name "Little Nell" as a stage name after her arrival in Britain in the early 1970s with her family. She sold clothes at Kensington Market; her stall was next to Freddie Mercury's. She also worked as a busker and as a soda jerk in a café, where her tap dancing is often noted as the reason why she was cast as Columbia in the original production of The Rocky Horror Show following an impromptu audition. She reprised the role in The Rocky Horror Picture Show, released in 1975, and starred as Nurse Ansalong in the 1981 sequel, Shock Treatment.

After The Rocky Horror Picture Show, she signed a recording contract with A&M Records. Her debut single was "Stilettos and Lipstick" backed with "Do the Swim", released in 1975. She also created a disco version of the song "Fever" in 1976 which was again backed with "Do the Swim". The B-side of both of these releases became better known, perhaps helped by a performance on British television in which she accidentally (and repeatedly) exposed her breasts. While edited out of the original broadcast in 1975, the unedited version was shown worldwide on bloopers shows (beginning with the British show It'll be Alright on the Night in 1977). Following this notoriety, another effort was made to promote the recordings made in 1975 and 1976. In 1978, a "triple B-side" titled The Musical World of Little Nell (Aquatic Teenage Sex & Squalor) was released which featured both "Do the Swim" and "Stillettos and Lipstick" along with the track "Dance that Cocktail Latin Way" (also known as "Tropical Isle") which originally appeared as the B-side of her second single from 1976. Following some success with the EP, the other two tracks, singles "Fever" and "See You Round like a Record", were released as a single but that was to be her last release on A&M. A final single, "Beauty Queen" from the film The Alternative Miss World, was released on PRE Records in 1980.

In 1986 she opened the nightclub Nell's on W. 14th St in Manhattan with Keith McNally and Lynn Wagenknecht.

In 1995 she opened two restaurants in New York: The Kiosk (uptown) and E&O (downtown). Nell's was sold in 1998 to Noel Ashman and his Business partner actor Chris Noth, right before she gave birth to daughter Matilda Violet in June 1998 to ex-boyfriend and Business partner Eamonn Roche.

Campbell has written several magazine articles, including regular segments called "MamaTalks" and "FirstLook" in the now defunct Talk magazine, starting in the December 1999 issue. She returned to Australia after selling her Boerum Hill house in Brooklyn in December 2005, and is now living with her daughter.