A film scenarist since 1915 (Body and Soul, The Builder of Bridges, The Great Divide), Kelly is best remembered as the author of the play Three Faces East, first presented on Broadway at the Cohan & Harris Theatre on August 13, 1918. The successful mystery melodrama was filmed as a silent in 1926, and as a talking feature by Warner Bros. Pictures in 1930. Following the play's debut, Kelly enlisted in the Navy and served for the rest of World War I. Afterward, he returned to writing screenplays that include Love's Redemption (1921), My Old Kentucky Home (1922), The Silent Command (1923), and The Scarlet West (1925).
In 1932, Kelly received treatment for tuberculosis at a hospital in Mount Vernon, New York. Terminally ill, he left the facility and returned to his apartment at 410 W. 110th Street in New York City. On the morning of September 26, 1932, Anna Delaforce, a longtime friend of Kelly's, received a letter from the scenarist informing her that he intended to end his life. In it, he asked that she notify his brothers and other friends of his death. Delaforce immediately contacted police, who forced entry into the 35-year-old writer's apartment. Inside the gas fume-filled rooms, the lifeless Kelly lay on a couch, the floor around him littered with the manuscript of Three Faces East and notes written for friends and the landlord. The writer left $27.00 to his landlord to cover any damage to the apartment. In an explanatory note addressed to police, Kelly wrote (in part): "This is a plain case of suicide. Having contracted an absolutely hopeless case of T.B. in both my lungs and intestines and since I have contracted it in my throat, I can see no sense in prolonging this agony any longer. I thought I could endure it a little longer but I can't...Give my belongings, such as they are, to the American Legion and kindly notify them that I requested that no religious services be held before my burial."