His other TV roles include Tycho Nestoris in Game of Thrones (2014–2017), Stephen Gardiner in Wolf Hall (2015), and Peter Mandelson in Coalition (2015).

He has acted in films such as Victor Frankenstein (2015), Denial (2016), Christopher Robin (2018), The Favourite (2018), The Father (2020), Operation Mincemeat (2021), and Mission: Impossible – Dead Reckoning Part One (2023).

On stage, Gatiss played Menenius in the revival of William Shakespeare's Coriolanus (2013) for which he earned a Laurence Olivier Award for Best Actor in a Supporting Role nomination.

He portrayed Sir John Gielgud in the Jack Thorne play The Motive and the Cue (2023) for which he earned the Laurence Olivier Award for Best Actor.

[5] His passions included watching Doctor Who and Hammer Horror films on television, reading Sherlock Holmes and H. G. Wells, and collecting fossils.

[13] Gatiss is a member of the sketch comedy team The League of Gentlemen (along with fellow performers Reece Shearsmith, Steve Pemberton and co-writer Jeremy Dyson).

[7] Shearsmith and Pemberton reunited in 2009 to create a similarly dark BBC sitcom, Psychoville, which featured an episode guest-starring Gatiss.

[14][15] Outside The League, Gatiss' television work has included writing for the 2001 revival of Randall & Hopkirk and script editing the popular sketch show Little Britain in 2003, making guest appearances in both.

Other acting appearances include the comedy-drama In the Red (BBC Two, 1998), the macabre sitcom Nighty Night (BBC Three, 2003), Agatha Christie's Marple as Ronald Hawes in "The Murder at the Vicarage", a guest appearance in the Vic & Bob series Catterick in 2004 and the live 2005 remake of the classic science fiction serial The Quatermass Experiment.

A second series of Nighty Night and the new comedy-drama Funland, the latter co-written by his League cohort Jeremy Dyson, both featured Gatiss and aired on BBC Three in the autumn of 2005.

He wrote and starred in the BBC Four docudrama The Worst Journey in the World, based on the memoir by polar explorer Apsley Cherry-Garrard.

Gatiss appears frequently in BBC Radio productions, including the science fiction comedy Nebulous and The Further Adventures of Sherlock Holmes story The Shameful Betrayal of Miss Emily Smith.

In 2009, he was The Man in Black when BBC Radio 7 revived the character (originally played by Valentine Dyall and Edward de Souza) to introduce a series of five creepy audio dramas.

In film, he has starred in Sex Lives of the Potato Men (2004) and had minor roles in Birthday Girl (2001), Bright Young Things (2003), Match Point (2005) and Starter for 10 (2006).

In the 2008 English language re-release of the cult 2006 Norwegian animated film Free Jimmy, Gatiss voiced the character of "Jakki," a heavy-set, bizarrely dressed biker member of the "Lappish Mafia."

[25] From December 2010 to March 2011, Gatiss was playing the role of Bernard in Alan Ayckbourn's Season's Greetings at the Royal National Theatre in London alongside Catherine Tate.

[26] From 18 October – 24 November that year he was Charles I in the Hampstead Theatre production of 55 Days by Howard Brenton, a play dramatising the military coup that killed a King and forged a Commonwealth under Oliver Cromwell.

[27] With Steven Moffat, with whom Gatiss worked on Doctor Who and Jekyll, he also co-created and co-produced Sherlock (2010) starring Benedict Cumberbatch and Martin Freeman.

It starred Sacha Dhawan, John Castle, Louise Jameson, Una Stubbs, David Ryall, Eleanor Bron, Nick Burns and Roy Barraclough.

[33][non-primary source needed] In the BBC's 2015 series Wolf Hall, Gatiss played King Henry VIII's secretary Stephen Gardiner.

They made history when the play transferred to the Vaudeville Theatre in 2017 as the first married gay couple to appear together on a West End stage.

[37] Kate Maltby of The Guardian wrote of his performance, "Productions of The Madness of George III live or die by their star, and Gatiss delivers a tour de force.

"[38] That same year he played a supporting role as John Churchill, 1st Duke of Marlborough in the Yorgos Lanthimos directed black comedy The Favourite (2018) starring Olivia Colman, Emma Stone, and Rachel Weisz.

[46] In May 2022, Gatiss directed The Unfriend, a new play by Steven Moffat at the Minerva Theatre, Chichester, starring Amanda Abbington, Frances Barber and Reece Shearsmith.

[54] At the age of eleven, Gatiss won a school literary competition with a short science fiction story "The Anti-Noise Machine", published in a booklet by Darlington Borough Council.

[58] Although he acted in the third series and proposed an ultimately unproduced episode for the fourth, involving Nazis and the British Museum, it took until 2010 for Gatiss to return as writer.

Gatiss wrote and performed in the comedy spoof sketches The Web of Caves, The Kidnappers and The Pitch of Fear for the BBC's "Doctor Who Night" in 1999 with David Walliams.

He penned the 2013 docudrama An Adventure in Space and Time, a drama depicting the origins of the series, to celebrate the show's fiftieth anniversary.

[60] It ended with a cameo by Gatiss's League of Gentleman castmate Reece Shearsmith, portraying Patrick Troughton, who played the Second Doctor.

The documentary followed Gatiss's directorial debut with an adaption of one of James's stories, "The Tractate Middoth", for BBC Two, which was broadcast on Christmas Day 2013.