| Year | Title | Role | Notes |
| 1980 | Grange Hill | Jill Harcourt | 3 episodes |
| 1986 | Henry's Leg | Noreen | Miniseries |
| 1987 | A Killing on the Exchange | Ellen | Miniseries |
| 1988–1995 | The Bill | Dr. Howard / Lisa / Maggie Fisher | 4 episodes |
| 1989 | Hannay | Kirsten Larssen | Episode: "The Terrors of the Earth" |
| The Play on One | Daniella | Episode: "These Foolish Things" |
| 1992 | Covington Cross | Helen | Episode: "Cedric Hits the Road" |
| 1993 | Foreign Affairs | Actress | TV film |
| Soldier Soldier | Ursula Kröhling | Episode: "Camouflage" |
| 1994 | Woman of the Wolf | Woman (voice) | TV film |
| Crocodile Shoes | Caroline Carrison | 5 episodes |
| 1995 | The Infiltrator | Anna | TV film |
| 1996 | The Knock | Katherine Roberts | 13 episodes |
| Last of the Czars | Alexandra (voice) | 3 episodes |
| The Fortunes and Misfortunes of Moll Flanders | Moll Flanders | Miniseries |
| 1997 | Weapons of Mass Distraction | Verity Graham | TV film |
| 1997–2009 | ER | Dr. Elizabeth Corday | 160 episodes |
| 2003 | Boudica | Boudica | TV film; a . Warrior Queen |
| 2005 | The Poseidon Adventure | Suzanne Harrison | TV film |
| Without a Trace | Lucy Costin | Episode: "Viuda Negra" |
| 2008 | Freezing | Serena Wilson | Episode |
| Lost in Austen | Mrs. Bennet | Miniseries |
| CSI: Crime Scene Investigation | Patricia Alwick | Episode: "Art Imitates Life" |
| 2008, 2010–2013, 2015 | Doctor Who | River Song | 15 episodes |
| 2009 | Hope Springs | Ellie Lagden | 8 episodes |
| 2009–2010 | FlashForward | Fiona Banks | 3 episodes |
| Law & Order: Special Victims Unit | Miranda Pond | 4 episodes |
| 2010 | Ben Hur | Ruth | Miniseries |
| 2011 | Private Practice | Dr. Marla Thomkins | 2 episodes |
| Marchlands | Helen Maynard | Miniseries |
| 2012 | Upstairs Downstairs | Dr. Blanche Mottershead | 5 episodes |
| Who Do You Think You Are? | Herself | Episode: "Alex Kingston" |
| NCIS | Miranda Pennebaker | Episode: "Gone" |
| 2013–2016 | Arrow | Dinah Lance | 7 episodes |
| 2014 | Chasing Shadows | Ruth Hattersley | Miniseries |
| 2015 | American Odyssey | Jennifer Wachtel | 2 episodes |
| 2016, 2021 | Blue Bloods | Commander Sloane Thompson | 2 episodes |
| 2016 | Transformers: Rescue Bots | Quickshadow (voice) | 5 episodes |
| Shoot the Messenger | Mary Foster | 8 episodes |
| Gilmore Girls: A Year in the Life | Naomi Shropshire | Miniseries |
| Crushed | Cricket Stella | Unaired Hulu pilot |
| 2017 | Penn Zero: Part-Time Hero | Vlurgen (voice) | Episode: "Mr. Rippen" |
| 2018–2022 | A Discovery of Witches | Sarah Bishop | 20 episodes |
| 2019 | The Widow | Judith Gray | 8 episodes |
| 2022 | Dodger | Lucifer | 2 episodes |
| Treason | Audrey Gratz | 5 episodes |
| 2024 | Douglas Is Cancelled | Sheila | Main role |
| 2025 | The Chelsea Detective | Ambassador Emily Morgan | Episode: "Deadlock" |
| 2025 | Strictly Come Dancing | Herself | Contestant; Series 23 |
