He has played Guy Secretan in Green Wing, Dan Moody in I'm Alan Partridge, Seán Lincoln in Episodes,[2] Bigwig in Watership Down, Postman Pat in Postman Pat: The Movie, Richard Pitt in Hang Ups, Andrew in Bliss (2018), and Nathan Stern in The Split (2018–2022).

After graduating from RADA in 1994, Mangan did not pursue lead roles on screen, preferring to take what he saw as the less limited opportunities on the stage.

He worked again for director Declan Donnellan at the Royal Shakespeare Company in School for Scandal, and at the Savoy Theatre in Hay Fever.

[citation needed] In 2008 he played the title role in The Norman Conquests, directed by Matthew Warchus, at The Old Vic and then at the Circle in the Square on Broadway.

[18] In 2009 Free Agents, a romantic black comedy starred Mangan, Sharon Horgan and Anthony Head.

Unlike most detective series Dirk Gently featured broadly comic touches and even some science fiction themes such as time travel and artificial intelligence.

He played the title role in "The Hunt for Tony Blair", a one-off episode of The Comic Strip Presents..., a British television comedy, which was first shown on Channel 4 on 14 October 2011.

It stars Mangan as the former British Prime Minister Tony Blair, who is wanted for murder and on the run as a fugitive.

[21][22] He appeared in Episodes, a British-American television comedy series created by David Crane and Jeffrey Klarik and produced by Hat Trick Productions.

[26] Episodes has received positive reviews by critics,[27] with many singling out Mangan, Tamsin Greig, and Matt LeBlanc's performances.

[28] In 2018 Mangan played the lead role in a black comedy TV series Bliss, created by American comedian David Cross, which was aired on Sky One[29] and released by the BritBox streaming service.

Bliss stars Mangan as Andrew, a fraudulent travel writer, who is struggling to maintain long-term relationships with two partners, Kim (Heather Graham) and Denise (Jo Hartley), who are not aware of one another.

[30][31] He co-wrote and starred in Hang Ups for Channel 4, which was adapted from the American comedy series Web Therapy.

[32] The show was first broadcast in 2018 and had an all-star cast, including David Tennant, Katherine Parkinson, Charles Dance and Richard E.

[51] The film was shot on floating sea ice off the coast of Greenland, and stars an acclaimed cast of actors and comedians including Mangan, Rhys Thomas, Mark Benton, Alexander Skarsgård and Helen Baxendale.

[52] In 2013, Mangan played Alastair Caldwell in Rush, a British-German biographical sports drama film centered on the rivalry between race car drivers James Hunt and Niki Lauda during the 1976 Formula One motor-racing season.

It was written by Peter Morgan, directed by Ron Howard and stars Chris Hemsworth as Hunt and Daniel Brühl as Lauda.

[59] Mangan was announced in January 2024 as being a new presenter on Global's Classic FM, specifically hosting a Sunday afternoon (4pm) show.

[8] From 17 February 2025 Mangan is to star in a new desert island comedy, alongside other "castaway" celebrities, from previous editions of the programme.

[68] In August 2014, Mangan was one of 200 public figures who were signatories to a letter to The Guardian expressing their hope that Scotland would vote to remain part of the United Kingdom in that year's referendum on the issue.