Much of Thompson's television work has gone unseen outside of Britain, such as BBC productions of "The Crucible", "Casualty", "Bomber Harris", "A Traveller in Time" and the comedy series "Nelson's Column". She showed up in the US on an episode of sister Emma's variety show "Thompson" and a Granada production, "Sherlock Holmes: The Master Blackmailer" (aired on PBS in 1993).
Her film career began slowly, with a bit part (as a Mission girl) in the comedy "The Missionary" (1981). She returned to stage and TV work until 1986, when she had another small role in "The Death of the Heart" and it was another five years before she resurfaced in the romantic comedy "Twenty-One", as the best friend of heroine Patsy Kensit. Film fame first arrived with the 1994 smash hit "Four Weddings and a Funeral", in which Thompson portrayed Lydia, bride number two. Next came a Jane Austen double-header: she was delightful as the hypochondriac sister of Anne Elliott (Amanda Root) in Roger Michell's "Persuasion" (1995) and gave a brilliant performance as the endearingly annoying Miss Bates in Douglas McGrath's "Emma" (1996). In the latter, Thompson's onscreen mother was played by her mum, Phyllida Law.