In 2017, Firth joined the cast of the HBO series Game of Thrones in Eastwatch, an episode of Season 7 as Archmaester Sandhu.
ɪn tˈuː θˈaʊzənd sˈɛvəntˌiːn, fˈɜːθ dʒˈɔɪnd ðə kˈæst ʌvðɪ ˌeɪtʃbˌiːˈoʊ sˈɪɹiz ɡˈeɪm ʌv θɹˈoʊnz ɪn ˈiːstwɑːtʃ, ɐn ˈɛpɪsˌoʊd ʌv sˈiːzən sˈɛvən æz ˌɑːɹtʃmˈaɪstɚ sˈændhuː.