Born in Remscheid in 2000, Henri Mertens gained early stage experience there. He studied acting in Bochum (2020–2024), receiving the Studienstiftung des deutschen Volkes scholarship. During studies, he performed at Schauspielhaus Bochum. His first fixed engagement was at Schauspiel Köln. He joins the Schauspielhaus Zürich ensemble in 2025/26.