Dreymon was born in Germany, and moved with his family to live in several countries throughout his youth. He has lived in Germany, France, Switzerland, and the United States. Due to his upbringing, Dreymon grew up as a polyglot and has achieved fluency in English, German, and French. As an actor, Dreymon studied in Paris, France, before moving to England while studying at Drama Centre London.
Dreymon started out as a stage performer, becoming involved in plays in Paris and London throughout his studies. He transitioned to the screen when he got the role of Alexandre in the French TV movie Ni reprise, ni échangée (2010). Dreymon acted alongside Matt Smith of Doctor Who fame for the TV movie Christopher and His Kind (2011). After his previous debut in French film, Dreymon also went on to portray Bruce in Sotto il vestito niente - L'ultima sfilata (2011).
He has taken part in numerous short films, and had roles in films such as Resistance (2011), Blood Ransom (2014), and Guys Reading Poems (2016). Dreymon received his first recurring role in a major television series when he signed on as Luke Ramsey in American Horror Story: Coven. Dreymon has since been given the lead role of Uhtred of Bebbanburg on The Last Kingdom series. He is set to appear as Lee Haze in the upcoming film, Heartlock.