His first foray into the film industry was providing the story for 1934's The Meanest Gal in Town, starring ZaSu Pitts and directed by Russell Mack.
After Society Smugglers, he wrote the story and co-wrote the screenplay (with Gordon Kahn) for Code of the Streets, a crime drama which stars Harry Carey, along with a group of young actors billed as the Little Tough Guys.
[16] That same year he would co-write (this time with Robert Lee Johnson) another screenplay featuring the Bowery Boys, Give Us Wings, directed by Charles Lamont.
[23] In 1944 he co-authored the screenplay for Dark Waters, a film noir starring Merle Oberon, Franchot Tone and Thomas Mitchell, based on the novel of the same name by Frank and Marian Cockrell.
[26] His first film written specifically for Universal, was an adaptation of the James Roland novel, This Way Out, late in 1944, titled The Suspect, for which he received good reviews.
[29] The following year, along with Sam Hellman, he would write the screenplay for the romantic screwball comedy, The Runaround, directed by Charles Lamont, and starring Ella Raines and Rod Cameron.
[31] With the advent of television, Horman would pen the first miniseries, The Living Christ, which consists of twelve half-hour episodes, and aired on NBC in 1951.