In 1924, the magazine Story World selected him on a list of the ten individuals who had contributed the most to the advancement of the motion picture industry from its inception forward.

While working in New York, a colleague showed him an advertisement by a motion picture company in the Saturday Evening Post inviting new authors to contribute stories.

His early films were mostly in the western genre, but also included historical dramas such as The Witch of Salem (1913) and The Battle of Gettysburg (1913), and comedies such as "The Adventures of Shorty" two-reelers from 1914 through 1917.

These included The Golden Claw and a series of screenplays for silent film femme fatale, Louise Glaum, such as The Wolf Woman (described as "the greatest vampire woman of all time"), Sahara and the provocatively titled Sex (featuring Glaum performing a sensual "spider dance" dressed in a form-fitting cloak of webs).

Perhaps Sullivan's most famous screenplay was Civilization, a big budget anti-war movie in which Jesus appeared on a World War I battlefield.

The commander is sentenced to death for refusing to follow orders, and at his execution, the spirit of Jesus emerges from his dead body and gives the king of the warring nation a tour of the battlefields.

[5] Sullivan returned to the subject of World War I as the supervising story chief for the 1930 film adaptation of All Quiet on the Western Front.

Sullivan prided himself on tackling a diverse range of subject matters, telling an interviewer the following:I have made all kinds and manner of pictures, none of them the work of a specialist in a certain grooved form.

The man who makes pictures for the public must be able to turn from comedy to melodrama, from psychological realism to sophisticated farce, from the big-scale popular spectacle to the cameo of emotions, sentimental drama.

The Los Angeles Times wrote of him:Several years ago, when the newly-formed Triangle organization contributed a new art and finish to the motion picture, there came into great prominence C. Gardner Sullivan, a writer of fine capabilities; a careful, technical craftsman.

He was given a roving commission by Ince allowing him to "leave the studio with a free mind and just browse around wherever fancy dictates; if the spirit should move him he may write a script now and then, 'just for practice,' or he may just store up a fund of mental notes for future use.

In February 1924, the Los Angeles Times reported that the number of feature films produced from the original stories or adaptations of Mr. Sullivan totaled 311 in eight years.

... Give the public a story that touches the heart and is true to life, and, to paraphrase Emerson, 'the world will make a beaten path to the theater box office.

His final film credit was the story of Jackass Mail, a 1942 western directed by Norman Z. McLeod and starring Wallace Beery.

[17] In 1924, the magazine Story World selected a list of the ten individuals who had contributed the most to the advancement of the motion picture industry from the time of its inception.