In October 2021, Fiennes Tiffin was announced among the cast of an upcoming historical drama entitled The Woman King, alongside Viola Davis, Jayme Lawson and Masali Baduza. In May 2021, Fiennes Tiffin was announced to be starring as the lead in the romantic drama First Love alongside Sydney Park.

He portrayed Brooks Gustafson in the thriller film The Silencing, released in July 2020. He returned for his role as Hardin Scott in the sequel, After We Collided, which was released in September 2020 and again reprises his role for the final sequels After We Fell and After Ever Happy which were filmed simultaneously in late 2020. The film was released in April 2019, grossing $69.7m worldwide. In 2018, Fiennes Tiffin was cast in the lead role of Hardin Scott in the film After, based on the New York Times best-selling book of the same name by Anna Todd. Yates described Fiennes Tiffin as 'very focused and disciplined' and said he 'got the corners and dark moods and odd spirit of the character' as well as having a 'wonderful haunted quality that seemed to bring Tom Riddle alive on-screen for us'. Director David Yates said he was cast due to his ability to find 'the darker space' in his line readings, and that he did not get the role due to his relation to Ralph Fiennes, his uncle who plays Voldemort, but admitted the family resemblance was a 'clincher'. He got the part of Tom Riddle (the young Voldemort) in Harry Potter and the Half-Blood Prince from thousands of young actors who auditioned for the role, though at least one publication alleged that his family connections alone landed him the part. He made his first film appearance as Spartak in the 2008 drama film Bigga Than Ben.

Prior to his acting career, Fiennes Tiffin worked jobs as a landscaper and caterer. His maternal grandparents were photographer Mark Fiennes and novelist Jennifer Lash. He is a member of the Twisleton-Wykeham-Fiennes family his great-grandfather was Sir Maurice Fiennes, while his uncles are actors Ralph and Joseph Fiennes. He was educated at Raey Primary School in Lambeth, Emanuel School in Battersea, and Graveney School in Tooting. According to a 2020 interview, he does not hyphenate his name because his parents were never married. He has an older brother named Titan and a younger sister named Mercy. Hero Fiennes Tiffin was born in London on 6 November 1997, the son of film director Martha Fiennes and cinematographer George Tiffin.

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