Sandemose went to sea in his teens, jumped ship in Newfoundland, and worked in a lumber camp before returning to Denmark with memories of violence and misery to write stories influenced by Jack London (London, Jack) and Joseph Conrad (Conrad, Joseph).

About 1930 Sandemose settled in Norway and during the 1930s published a series of partly autobiographical novels, bitterly castigating the convention-ridden, small-town society of his Danish childhood and drawing on violent episodes from his later wanderings. He is often mentioned as the scribe of “Jante's Law,” whose 10 commandments are formulated in his best novel, En flyktning krysser sit spor (1933; A Fugitive Crosses His Tracks). The first commandment reads “You shall not believe you are special,” and the others are similar expressions of the fictional town of Jante's unmitigated repression of the individual.

Among Sandemose's other works are En sjømann går iland (1931; “A Sailor Disembarks”) and Der stod en benk i haven (1937; “A Bench Stood in the Garden”). His later novels include Det svundne er en drøm (1946; “The Past Is a Dream”), Varulven (1958; The Werewolf), and its continuation, Felicias Bryllup (1961; “Felicia's Wedding”). In these works, the dualism of good and evil is a recurrent theme.