Scott was born in Arlington, New Jersey, the son of successful Irish Catholic parents — his father worked in middle management for the New York Telephone Company. Arlington was one of the centres of the American textile industry, a key site in the history of industrial capitalism and a hotbed of radical labour agitation. Arlington is 12 miles south of Paterson, where the 1913 strike of 25,000 silk workers brought together socialists, Wobblies and Greenwich Village intellectuals. In 1926, when Scott was 15, 20,000 textile workers in nearby Passaic, New Jersey, closed down the mills.
Scott's his older brother Allan was a playwright (and later screenwriter) whose comedy Goodbye Again ran on Broadway for most of 1933.
Adrian's college yearbook in Amherst College described him: "Hat cocked back at a rakish angle, cigar in the corner of his mouth, his fingers playing nimbly over the typewriter keys, the inimitable R.A.L. Scott."
After graduating from Amherst in 1934, at the lowest point of the Depression, Scott followed his brother west to seek his fortune in Hollywood. He was the producer of the film noirs Murder, My Sweet (1944), Cornered (1945), and Crossfire (1947), all of which were directed by Edward Dmytryk. Crossfire was nominated for the Academy Award for Best Picture.
Scott joined the Communist Party USA in 1944. In October 1947, Scott was called to testify during the House Committee on Un-American Activities (HUAC) hearings on Hollywood but – as did nine others – refused to testify and was sentenced to jail. Edward Dmytryk, another of these Hollywood Ten, later, in 1951 testified before the HUAC that Scott pressured him to put communist propaganda in his films.
Scott was subsequently blacklisted and, while he was unable to work in Hollywood, wrote pseudonymously for the British television series The Adventures of Robin Hood.
He was married to the actress, Anne Shirley, who subsequently married another screenwriter, Charles Lederer, nephew of Marion Davies. He later married Joan Scott (née LaCour), fellow screenwriter and producer. Joan sometimes served as Adrian's front when he was unable to publish under his own name, and later the surname LaCour was used by both when writing in Hollywood. He attempted to make a return to feature film production in 1967 by producing a new adaption of Monsieur Lecoq; the film was never finished. Film stills featuring the movie's actress Julie Newmar were featured in the September 1969 edition of Playboy.
Adrian was the brother of screenwriter Allan Scott, who is the father of actress Pippa Scott.
Adrian Scott died in 1972 in Sherman Oaks, California. Shortly before his death, Scott made a television adaption of The Great Man's Whiskers and was credited with his legal name.