Gilks began his career in cinematography in 1918 while serving as a member of the Field Photographic Unit of the Office of Strategic Services.

[1][2] Gilks worked on many silent films in the 1920s, such as Red Hair (1928) with Clara Bow and the historical epic Old Ironsides (1926) starring Esther Ralston.

He also worked on well-known sound films such as Miss Fane's Baby Is Stolen (1934), Ruggles of Red Gap (1935), several of the Dr. Kildare movies, and his Oscar-winning work on An American in Paris (1951).

Gilks shared the Best Cinematography Academy Award for An American in Paris with John Alton.

[3] His last credit was for second unit photography on John Ford's seminal The Searchers (1956).