He moved to Newark, New York in 1907, and nine years later his older sister, Thelma, and younger brother, Richard, were killed while riding in a car that was struck by an express train.
On September 21, 1968, Jackson died of barbiturate poisoning at St. Vincent's Hospital in New York City. His death was ruled a suicide. At the time of his death, Jackson was working on a sequel to "The Lost Weekend" entitled "Farther and Wider".
According to author and scholar Anthony Slide, Jackson had relapsed into alcoholism around the time of his death and had become estranged from his wife and children. Slide also wrote that Jackson had been closeted for the majority of his life and, in his later years, attempted to come to terms with his bisexuality. Slide maintains that Jackson "[...] identified as bisexual late in life" and began living with his male lover in 1965.