Born and raised in Melbourne, Walker became interested in photography while a student in high school. After graduation she studied film criticism and cinema studies with John Flaus, who introduced her to several people working in the industry. She apprenticed as an unpaid assistant on several documentaries and music videos before shooting her first feature film, Return Home, at the age of twenty-five. Additional screen credits include Parklands, The Well, Lantana, Australian Rules, Shattered Glass, and Australia. Her television credits include the Australian Broadcasting Corporation series Raw FM.
Walker has filmed commercials for Nike, Toyota, Caltex, Cingular Wireless, Foxwoods Casino and, most notably, the spot for Chanel No. 5 directed by Baz Luhrmann and featuring Nicole Kidman.
The Australian Cinematographers Society honored Walker with their Award of Distinction for Parklands and Lantana. She was nominated for the Australian Film Institute Award for Best Achievement in Cinematography for The Well, the Film Critics Circle of Australia Award for Best Cinematography for The Well and Lantana, and the Independent Spirit Award for Best Cinematography for Shattered Glass.
Walker presently lives in Santa Monica, California.