Carter was a musical performer in New York on and off-Broadway throughout most of the 70s, beginning with the musical "Soon" (1970), better known for launching Richard Gere. She was in the ensemble cast of "Don't Bother Me, I Can't Cope" in the early 70s at the Edison Theatre, and in 1977 joined the Manhattan Theatre Club presentation of "Ain't Misbehavin'", a collection of the works of Fats Waller, emerging from the show as a hot property. Although she had briefly been in the cast of the ABC daytime drama "Ryan's Hope" in 1975, Carter had not been on a primetime series until NBC slotted her into "Lobo" in 1980, as a sassy police sergeant. The low-brow series faltered and the following season Carter starred in "Gimme a Break" (1981-87), an NBC sitcom in which she was a singer who had become the housekeeper for the police chief in a small California community. Carter also sang the show's title song. By the time the series ended, her character had moved to New York City. In 1990, she was in the short-lived series "You Take the Kids" and from 1993 to 1995, she appeared in the recurring role of Mark Curry's boss in the ABC sitcom "Hangin' with Mr. Cooper". Carter also appeared in a few TV-movies, including the musical "Cindy" (ABC, 1978), in which billed as Nell-Ruth Carter she played one of the stepsisters in a send-up of the Cinderella story. She also played the mother of ill-fated athlete Hank Gathers in "Final Shot: The Hank Gathers Story" (syndicated 1992) and was a diva who hires Dinah Manoff as a servant and then gets handcuffed to her as they flee for their lives in "Maid for Each Other" (NBC, 1992). Carter's appearances in musical specials have also been numerous, among them a guest appearance on "Baryshnikov on Broadway" (ABC, 1980); recreating her stage role in "Ain't Misbehavin'" (NBC, 1981); and as one of the performers in "Evening at the Pops" (PBS, 1987).
Carter's feature film appearances have been limited. She was a singer in the "Black Boys/White Boys" number in Milos Forman's "Hair" (1979), and played small roles in "Modern Problems" and "Back Roads" (both 1981). In 1992, Carter offered one of the key voices for the animated feature "Bebe's Kids". She has also performed in Las Vegas, headlined a 1991 Los Angeles revival of "Hello, Dolly!" with an African-American cast and played the villainous Miss Hannigan in the 1996-97 revival of the stage musical "Annie".