Her first BAFTA nomination, Campbell earned the previous year for Eileen Everson, a very different character, opposite Bob Hoskins in Dennis Potter's television serial Pennies from Heaven (1978). Campbell's one other role in a work by Potter is as Janet in Rain on the Roof (1980).

Campbell's other stage performances in London have encompassed the classics as well as new plays; they include You Never Can Tell (Lyric, 1979); Miss Julie (1983) in the title role; Little Eyolf (1985) as Asta; The Daughter-in-Law (1985) as Minnie; The Sneeze (a Chekhov selection) (1988) in various roles; Betrayal (1991) as Emma; The Strip (1995) as Loretta; Some Sunny Day (1996) as Emily; The Seagull (1997) as Arkadina; Passion (2000) as Nell; and Life After George (2002) as Beatrix.

Campbell is stage performer of considerable note and great range. She has been twice a member of the Royal Shakespeare Company. At the RSC in 1982, she played Nora Helmer in Adrian Noble's memorable production of Ibsen's A Doll's House (for which she was awarded the Laurence Olivier Award for Best Actress in a Revival). In that same season, she also appeared as Diana in All's Well That Ends Well.

She returned to the RSC in the 1992–94 season, playing Lady Macbeth to Sir Derek Jacobi's lead in Noble's controversial production of Macbeth; Beatrice-Joanna in The Changeling; Mistress Ford in The Merry Wives of Windsor and Natasha in Misha's Party. She worked at the Royal National Theatre: playing as a junior member of the company in 1975, as Freda in Sir Peter Hall's Old Vic production of John Gabriel Borkman (starring Sir Ralph Richardson, Dame Peggy Ashcroft and Dame Wendy Hiller) and as Maggie in W. S. Gilbert's Engaged; in 1995, as Lady Politic Would-Be in Matthew Warchus's Volpone; and in 2003 as Dotty Otley in the NT's touring (and London) revival of Noises Off.