For the American Cinema Editors Award for Best Edited Feature Film – Dramatic he has received a string of six nominations and in 2016[1] he won, for Arrival.

[6][7] Walker started as a Sound Editor, coaxing animal impersonator Percy Edwards out of retirement to provide gorilla noises for Philip Saville's series First Born (1988), his first collaboration with composer Hans Zimmer.

After his first forays as a Film Editor, cutting classical music documentaries for the BBC, Walker broke into editing drama with Julian Farino's Out of the Blue and comedy with two series of David Renwick's Jonathan Creek.

Their third collaboration was 12 Years a Slave (2013), the true story of Solomon Northup, a free man kidnapped and sold into slavery, set in 1840s Louisiana.

12 Years a Slave (2013) won three Academy Awards: Best Picture, Best Supporting Actress for Nyong'o, and Best Adapted Screenplay for John Ridley.

Their first, Sicario, is a 2015 American crime-thriller drama film starring Benicio del Toro and Josh Brolin in which an idealistic FBI agent Emily Blunt is enlisted in a secret CIA op to bring down the head of a brutal Mexican drug cartel.

"[15] In 2010, Walker cut the documentary-feature Life in a Day for Academy Award-winning director Kevin Macdonald and producer Ridley Scott.

[16][17] Walker has edited many British Indie features such as The Escapist (2008) written and directed by Rupert Wyatt; Harry Brown (2009), starring Michael Caine as a modern-day vigilante; and Brighton Rock (2010), a reworking of the Graham Greene classic that set the action against a backdrop of the Mod and Rocker riots of 1964.

Walker has cut many British TV programs: Jimmy McGovern's The Lakes; Eroica for the BBC; ITV blockbuster Doctor Zhivago starring Sam Neill and Keira Knightley; Sword of Honour for Channel 4, starring Daniel Craig; The Devil's Whore, for director Marc Munden and Tommy Tiernan for director Richard Ayoade.