| Year | Title | Role | Notes | Ref. |
| 2003 | The Shield | Jessica Hintel | Episode: "The Quick Fix" | |
| American Dreams | Amy Fielding | Episode: "Act of Contrition" | |
| The O'Keefes | Virginia's Owner | Episode: "Substitute Teacher" | |
| Everwood | Stacey Wilson | Episode: "Extra Ordinary" | |
| 2004 | Deadwood | Flora Anderson | 2 episodes | |
| Gracie's Choice | Gracie Thompson | TV movie | |
| 2004–2007, 2019 | Veronica Mars | Veronica Mars | Lead role; also executive producer (season 4) | |
| 2007–2008 | Heroes | Elle Bishop | Main cast (season 2); Recurring (season 3) | |
| 2007–2012 | Gossip Girl | Gossip Girl (voice) / Herself | Uncredited; Herself (Episode: "New York, I Love You XOXO") | |
| 2009 | The Cleveland Show | Mandy (voice) | Episode: "Da Doggone Daddy-Daughter Dinner Dance" | |
| 2009–2010 | Party Down | Uda Bengt | 2 episodes | |
| 2011 | Glenn Martin, DDS | Hayley (voice) | Episode: "Videogame Wizard" | |
| Robot Chicken | Sara Lee (voice) | Episode: "Some Like It Hitman" | |
| 2012–2016 | House of Lies | Jeannie van der Hooven | Lead role (5 seasons) | |
| 2012 | Unsupervised | Megan (voice) | 13 episodes | |
| 2012–2014 | CMT Music Awards | Host | Special | |
| 2013–2014 | Parks and Recreation | Ingrid de Forest | 3 episodes | |
| 2013, 2020 | Hollywood Game Night | Herself | 2 episodes | |
| 2013 | Lady Gaga and the Muppets Holiday Spectacular | Special | |
| 2015 | Repeat After Me | Episode: "1 " | |
| Liv and Maddie | Episode: "Ask Her More-a-Rooney" | |
| 30th Independent Spirit Awards | Herself / Co-Host | Special, with Fred Armisen | |
| It's Your 50th Christmas, Charlie Brown | Special | |
| 2015, 2021 | The Simpsons | Harper Jambowski (voice), Marge Simpson (singing voice) | Episodes: "Friend with Benefit", "The Star of the Backstage" | |
| 2016 | iZombie | Herself (voice) | Episode: "Fifty Shades of Grey Matter" | |
| LEGO Frozen Northern Lights | Anna (voice) | Special | |
| 2016–2020 | The Good Place | Eleanor Shellstrop | Lead role: 53 episodes ; Directed episode: "The Funeral to End All Funerals" | |
| 2017 | Nobodies | Herself | Episode: "Too Much of a Good Thing" | |
| Jimmy Kimmel Live! | Herself / Guest Host | May 4, 2017; standing in for Jimmy Kimmel | |
| BoJack Horseman | Ruthie (voice) | Episode: "Ruthie" | |
| Family Guy | Martha (voice) | Episode: "Petey IV" | |
| Encore! | Herself / Host | Also executive producer | |
| 2017–2018 | Big Mouth | Various voices | 4 episodes | |
| 2018 | 24th Screen Actors Guild Awards | Herself / Host | Special | |
| The Ellen DeGeneres Show | Herself / Guest Host | May 31, 2018; standing in for Ellen DeGeneres | |
| The Joel McHale Show with Joel McHale | Herself | Episode: "Pizza Ghost" | |
| 2019 | Last Week Tonight with John Oliver | Episode: "Compounding Pharmacies" | |
| 2019–2020 | Encore! | Herself / Host | 12 episodes Also executive producer | |
| 2020 | : The Nickelodeon Town Hall | Moderator of COVID-19 special; Also executive producer | |
| Into the Unknown: Making Frozen 2 | Herself | Documentary | |
| 2020, 2022 | Central Park | Molly Tillerman (voice), Abby (voice) | Main role (season 1 and 3) | |
| 2021–2023 | Gossip Girl | Gossip Girl (voice) | Narrator | |
| 2021 | Ultra City Smiths | Donella Pecker (voice) | Main role | |
| HouseBroken | Juliet (voice) | Episode: "Who's a Good Therapist?" | |
| 2021–2022 | Do, Re & Mi | Mi (voice) | Main role; also executive producer | |
| 2022–2023 | The Tiny Chef Show | Herself | 3 episodes; also executive producer | |
| 2022 | The Woman in the House Across the Street from the Girl in the Window | Anna Whitaker | Miniseries; main role; also executive producer | |
| Norman Lear: 100 Years of Music & Laughter | Herself | Television special | |
| Zootopia+ | Priscilla (voice) | Episode: "Dinner Rush" | |
