Film:
* The King's Speech (2010) - as The Duke of York / King George VI
* Skyfall (2012) - as Tanner
* The Imitation Game (2014) - as Hugh Alexander
* The Woman in Black (2012) - as Arthur Kipps
* The Woman in Black: Angel of Death (2015) - as Arthur Kipps
* Our Kind of Traitor (2016) - as Perry
* The Darkest Hour (2017) - as Clement Attlee
* The Guernsey Literary and Potato Peel Pie Society (2018) - as Dawes
* Finding Neverland (2004) - as Arthur Conan Doyle
* The Last Station (2009) - as Leon Trotsky
* Green Room (2015) - as Pat
* The Death of Stalin (2017) - as Nikita Khrushchev
* The Personal History of David Copperfield (2019) - as Mr. Micawber
* The Courier (2020) - as Greville Wynne
* The Outfit (2022) - as Francis
* The Electrical Life of Louis Wain (2021) - as Sir William Gosse
* The Batman (2022) - as The Penguin (voice)
* The Banshees of Inisherin (2022) - as Domhnall
* The Wonder (2022) - as William Byrne
Television:
* Penny Dreadful (2014-2016) - as Dr. Victor Frankenstein
* Black Mirror (2011-present) - as "White Bear"
* The Government Inspector (2010) - as Hlestakov
* The Mystery of Edwin Drood (2012) - as John Jasper
* Luther (2010-2019) - as DS Ian Reed
* Quiz (2020) - as Charles Ingram
* The Crown (2016-present) - as Lord Ivar Mountbatten
* The Serpent (2021) - as Herman Knippenberg
* The Power (2023) - as Robert Le Doux
This is not an exhaustive list, but it covers many of his notable roles across both film and television. You can find a more complete list of his credits on IMDb or other film databases.