Mark Day (born 22 February 1961) is a British film editor. He won two BAFTA Awards for Best Editing for State of Play and Sex Traffic, both directed by David Yates with whom Day also worked with on The Way We Live Now, The Young Visiters and The Girl in the Café; the former two projects gained Day two Royal Television Society award nominations for Best Tape and Film Editing along with two BAFTA nominations and the latter project gained Day a Primetime Emmy Award nomination for Outstanding Single-Camera Picture Editing. Day also worked with Yates on The Sins and the final four Harry Potter films: Order of the Phoenix, Half-Blood Prince, Deathly Hallows – Part 1 and Deathly Hallows – Part 2. Day has edited over thirty television films and dramas.

Filmography