Harriet Marston Slater (born 28 November 1994) is an English actress. On television, she is known for her roles in the DC Universe series Pennyworth (2019–2022) and the MGM+ period drama Belgravia: The Next Chapter (2024).

She was named a 2023 Bright Young Thing by Tatler Slater was born and raised in Leicester. Her extended family were active in amateur dramatics. She joined a local youth theatre group called the Little Theatre at the age of 6.