His work is stylised by its blending of traditional orchestration with contemporary electronic elements. Jóhannsson released solo albums from 2002 onward. In 2016, he signed with Deutsche Grammophon, through which he released his last solo album, Orphée. Some of his works in film include the original scores for Denis Villeneuve's Prisoners, Sicario, and Arrival, and James Marsh's The Theory of Everything.

His only directorial work, Last and First Men, premiered at the Manchester International Festival in 2017, where he also performed the score live with the BBC Philharmonic Orchestra.