One of Wanamaker's earliest appearances on American TV was as Annemarie Kempf in the NBC miniseries "Inside the Third Reich" (1982), and her British TV series "Paradise Postponed" (1986) aired on "Masterpiece Theatre" (PBS). She became a national favorite in the UK for her continuing role opposite Adam Faith in the BBC-1's "Love Hurts" (1992-1994) and co-starred as the girlfriend of a possible killer in the first installment of the popular "Prime Suspect" series, seen in the USA in 1992 on PBS' "Mystery!". Wanamaker then went on to act in three "Masterpiece Theatre" productions, "Memento Mori" (1992), "The Countess Alice" and "The Blackheath Poisonings", as well as in the "Fat Chance" episode of the "Inspector Morse" series on "Mystery!" (all 1993).

Her work for the screen not withstanding, Wanamaker has remained first and foremost a stage actor. She lent her strong persona to a London production of Arthur Miller's "The Crucible" and reinterpreted the role of Amanda Wingfield in an acclaimed 1995 revival of "The Glass Menagerie". After collecting three nominations for the Olivier Award, the actress finally took home 1998's honor for Best Actress in a Play as Sophocles' "Electra" (1997). Though her appearances in features have been relatively infrequent, 1997 saw her in two, "Swept From the Sea" and "Wilde", for which she received a BAFTA nomination as a witty member of Oscar Wilde's circle who supported the writer and his family after accusations of gross indecency precipitated his fall from grace. She was also on hand that year for the official opening of the Globe Theatre, delivering a short prologue honoring the realization of her father's lifelong dream. In 2001, Wanamaker played Madame Hooch, the Quidditch referee, in "Harry Potter and the Sorcerer's Stone".