| Year | Title | Role | Notes |
| 2005 | Ahead of the Class | Vicky Foley | Television film |
| Casualty | Helen Gibbons | Episode: "The Long Goodbye" (uncredited role) |
| Extras | Woman in Queue | Episode: "Ross Kemp & Vinnie Jones" |
| 2005–2009 | Doc Martin | Pauline Lamb | Series 2-4 & Christmas special, 24 episodes |
| 2006 | Comedy Lab | Various roles | Episode: "Slap" |
| 2006–2010, 2013 | The IT Crowd | Jen Barber | British Comedy Award for Best Television Comedy ActressNominated – BAFTA for Best Female Comedy PerformanceWinner of BAFTA award Best Female Performance in a Comedy Programme 2014 |
| 2007 | Fear, Stress & Anger | Gemma | 5 episodes |
| Love Triangle | Patty (voice) | Television short film |
| Christmas at the Riviera | Vanessa | Television film |
| 2007–2009 | Katy Brand's Big Ass Show | Various characters | 18 episodes |
| 2009 | Jonathan Creek | Nicola | Episode: "The Grinning Man" |
| 2009–2010 | The Old Guys | Amber | 8 episodes |
| 2010 | The Great Outdoors | Sophie | 3 episodes |
| Whites | Caroline | 6 episodes |
| 2011 | Psychoville | Fiona | Episode: "The Hunt" |
| Comedy Showcase | Pip | Episode: "Coma Girl" |
| 2011–2012 | The Bleak Old Shop of Stuff | Conceptiva | 4 episodes |
| 2011, 2015 | Would I Lie to You? | Herself - Panellist | Series 5, Episode 3 Series 9, Episode 2 |
| 2012 | Sherlock | Kitty Riley | Episode: "The Reichenbach Fall" |
| 2013 | Love Matters | Jo Pepper | Episode: "Officially Special" |
| 2014 | Cardinal Burns | Super Computer (voice) | Series 2, Episode 4 |
| The Honourable Woman | Rachel Stein | Mini-series; 8 episodes |
| Inside No. 9 | Rebecca | Episode: "Sardines" |
| Crackanory | Herself - Storyteller | Series 2, Episode 3: "The Crisis Plan" |
| 2014–2016 | In the Club | Kim Hall | 12 episodes |
| 2015 | Horizon | Herself - Narrator | Episode: "Which Universe Are We In?" |
| The Kennedys | Brenda Kennedy | Lead role; 6 episodes |
| 2015–2018 | Humans | Laura Hawkins | Lead role; 24 episodes |
| 2017 | Urban Myths | Ange | Episode: "Bob Dylan: Knockin' on Dave's Door" |
| 2018 | Hang Ups | Karen Muller | 6 episodes |
| 2018–2019 | Defending the Guilty | Caroline Bratt | Lead role; 7 episodes |
| 2020 | Unprecedented | Liz | Series 1, Episode 3 |
| Taskmaster | Herself - Contestant | Series 10, 10 episodes |
| Pandemonium | Rachel Jessop | One-off BBC One comedy (pilot episode of Here We Go) |
| 2021 | Sitting | Mary | TV adaption of Parkinson's 2018 stage play for BBC Four |
| Spreadsheet | Lauren | Lead role; 8 episodes |
| Hitmen | Kat Gaitskill | 5 episodes |
| 2022 | Travel Man | Herself | Travel documentary |
| 2022–present | Here We Go | Rachel Jessop | Lead role; 13 episodes |
| 2023 | Significant Other | Anna | 6 episodes |
| 2024 | Inside No. 9 | Herself | Series 9, Episode: "Plodding On" |
| Rivals | Lizzie Vereker | 8 episodes |
| 2027 | Harry Potter † | Molly Weasley | Filming |
| TBA | The Dream Lands † | Antonia | Filming |
