Mitchell began his acting career in 2015, upon graduating high school, appearing in short film Stereotype (voice only) and in the starring role of short film Fire.
2017
He is known for his roles in the ITV drama The Halcyon (2017), the medieval series The Last Kingdom (2017–2022), the BBC war drama World on Fire (2019–), and the HBO fantasy series House of the Dragon (2022–).
He later had a minor role in the film Just Charlie (2017) by Rebekah Fortune and appeared in a supporting role opposite Robert Pattinson and Mia Goth in High Life (2018) by Claire Denis.
In 2022, he was cast in an Amazon Prime Video original film, Emerald Fennell's Saltburn.
On television, Mitchell made his debut in the 2017 ITV period drama The Halcyon as Billy Taylor.
He had his breakout role in the BBC Two and Netflix historical drama The Last Kingdom as Osferth, a role he played from the second to fifth series.
2018
His films include High Life (2018) and Saltburn (2023).
Mitchell has stated in an interview that he grew up in Derby, and has one sibling, an older brother.
He trained at the Central Junior Television Workshop in Nottingham.
2019
In 2019, he starred as Tom Bennett in the BBC One World War II drama series World on Fire.
In 2022, Mitchell appeared in the ITV crime thriller Trigger Point as Billy Washington.
Later that year, Mitchell began playing Prince Aemond Targaryen in the HBO fantasy series House of the Dragon, a Game of Thrones prequel and adaptation of George R. R. Martin's fictional history book Fire and Blood.
His performance in the series received critical acclaim.