Porter emigrated to the United States as a young sailor and worked as a mechanic before joining the laboratory of Thomas Alva Edison in 1895/96. While working there until 1911, Porter revolutionized filmmaking. He directed the first U.S. documentary film, The Life of an American Fireman, in 1903. Into stock footage of actual fire scenes, he interpolated scenes of actors playing a fire-chief hero and a trapped mother and child. To heighten suspense, he cut back and forth from the terrified mother to the coming rescuers.

Porter's The Great Train Robbery (1903) was the most successful and influential of the early story films and established Porter as an outstanding figure in motion pictures. The eight-minute film depicts a robbery, the formation of a posse, and its pursuit and elimination of the gunmen. It standardized the length of the U.S. film, set the pattern for the western, used the first close-up—a shot of a gunman shooting—and gave the impetus for other directors to explore the function and power of film editing and camera placement. In 1907 Porter gave D.W. Griffith (Griffith, D W) his first acting role, in Rescued from an Eagle's Nest. Porter left the Edison Company in 1911 to found his own company, Rex Films, but the next year he joined Adolph Zukor's Famous Players Film Company. After directing his last film, The Eternal City (1915), he retired from moviemaking.