He first received acclaim for his 1890 novel Sult, translated as Hunger. The work, which is semi-autobiographical, described a young writer's descent into near madness as a result of hunger and poverty. In many ways, the novel presages the writings of Franz Kafka and other twentieth-century novelists, who explored the madness of the contemporary human condition. The book has since become one of the most influential novels of the 20th century.
Other important works by Hamsun include Pan (1894) and The Growth of the Soil (1917), for which he received the Nobel Prize in literature in 1920.
Despite his immense popularity in Norway and around the world, Hamsun's reputation waned considerably because of his support of Vidkun Quisling's Nazi regime during World War II. Following a meeting with Joseph Goebbels in 1943, he sent Goebbels his Nobel Prize medal as a gift. On the other hand, he also met with Adolf Hitler and tried to have him remove Josef Terboven from the position of Reichskommissar of Norway.
After the war, he was confined for several months in a psychiatric hospital for tests to determine his sanity. However, in 1948 he was fined 325,000 kroner for collaboration.