Mark Day is an English film and sound editor. He made his editorial contribution in nearly 45 movies and television series. He has won two BAFTA Awards for his editorial credits and also earned various other nominations. He is best known for his film editing works in the Harry Potter and Fantastic Beasts film series and The Legend of Tarzan (2016). His 2019 project includes Downton Abbey, a drama film directed by Michael Engler.