Lemarquis was born in Reykjavík, the son of an Icelandic mother and a French father, Gérard Lemarquis, who is a schoolteacher. His most distinguishing physical feature—a complete lack of hair of any kind—is the result of alopecia universalis, which made him completely hairless by the age of 14. He grew up between Iceland and France, and studied theater at the Cours Florent in Paris, where he was a classmate of actress Audrey Tautou. He also attended the Reykjavík School of Fine Arts in Iceland.

Lemarquis is possibly best known for his starring role in the 2003 Icelandic film Nói Albínói (e. Noi the Albino). Lemarquis' played a lead role in the 2018 Berlinale Film Festival winner, Touch Me Not. He has also appeared in films such as Snowpiercer, X-Men: Apocalypse and Blade Runner 2049.