She gained recognition and acclaim for her role as Elizabeth Bennet in the BBC miniseries Pride and Prejudice (1995), for which she received the British Academy Television Award for Best Actress.

She has also appeared in various television programs, including NBC's The Blacklist (2014–2015), the Hulu limited series The Looming Tower (2016), the Showtime miniseries The Comey Rule (2020), and the CBS legal drama The Good Fight (2022).

[9] Ehle made her West End debut as Elmire in the 1991 Peter Hall Company production of Tartuffe, for which she won second prize at the Ian Charleson Awards.

[10][11] Hall then cast her as Calypso in The Camomile Lawn (1992), a television adaptation of Mary Wesley's book of the same name, in which she and her mother played the same character at different ages.

In 2000, Ehle made her Broadway debut to great critical acclaim as Annie in Tom Stoppard's The Real Thing, winning the Tony Award for Best Performance by a Leading Actress in a Play.

[14] That following year, Ehle appeared again on Broadway in the revival of Noël Coward's Design for Living co-starring with Dominic West and Alan Cumming.

[20] Since 2010, Ehle has appeared in the critically acclaimed films The King's Speech (where she reunited with her Pride and Prejudice co-star Colin Firth), Steven Soderbergh's Contagion (2011), George Clooney's The Ides of March (2011), Kathryn Bigelow's Zero Dark Thirty (2012), Alan Rickman's A Little Chaos (2015), Terence Davies's A Quiet Passion (2016), and Ira Sachs's Little Men (2016).

TIME film critic Stephanie Zacharek described her as "superb" and Justin Chang writing for NPR declared her performance "quietly heartbreaking".

The series won a Peabody Award "For aptly packaging a bold adaptation of this twinned-body horror classic within the continued nightmarish world of women’s reproductive health care in the United States.

"[25] In 2024, Ehle appeared in four episodes of Law & Order:Organized Crime as Meredith Bonner, the Police Chief of Westbrook, Pa., who assists Elliot Stabler (Christopher Meloni) with the search for a serial killer.