He travelled to the Baltic Sea with his brother, and canoed along the Danube to the Black Sea. He spent time in Italy after taking his Abitur in 1937, where he wrote his first book, Tage und Nächte steigen aus dem Strom. Eine Donaufahrt. ("Days and nights rise from the river. A travel on the Danube."), published in 1941. He studied art in Dresden and Munich in 1939, and volunteered to join the Kriegsmarine in 1940.
As a Leutnant in the autumn of 1941, Buchheim joined Lieutenant-Commander Heinrich Lehmann-Willenbrock and the crew of U-96 for a single patrol in the Battle of the Atlantic. His orders were to photograph and describe the U-boat in action. From his experiences, he wrote a short story, Die Eichenlaubfahrt (The Oak-Leaves Patrol) - Lehmann-Willenbrock had been awarded the Knight's Cross with oak leaves. He ended the war as an Oberleutnant.
Buchheim is best known from the 1973 novel based on his wartime experiences, Das Boot ("The Boat"). Das Boot was a fictionalised autobiographical account, narrated by a "Leutnant Werner". It is said to be the best-selling German account of the Second World War, and was quickly translated into an English edition.
His novel was followed by a non-fiction work, U-Boot-Krieg (U-Boat War) in 1976, which became the first part of a trilogy, together with U-Boot-Fahrer (U-Boat Sailors), and Zu Tode Gesiegt (Victoried to Death), both published in 1998. The trilogy includes over 5,000 photographs taken during World War II. He is also the author of the novels Die Festung (1995) (The Fortress), based on travels home across France in 1944, and Der Abschied (2000) (The Parting), about the nuclear-powered cargo vessel NS Otto Hahn.
Das Boot was turned into a film in 1981, featuring Jürgen Prochnow as the captain and the debut of Herbert Grönemeyer as "Leutnant Werner". Director Wolfgang Petersen and Buchheim fell out after the author was not allowed to write the script. (Buchheim was always noted for his short temper - he was later nicknamed the "Starnberg volcano".) The film was the most expensive German film ever made. It was nominated for six Oscars.
The Buchheim Museum of Imagination opened in Bernried on the shore of Lake Starnberg in 2001, funded by the government of Bavaria. The entire collection has been estimated to be worth up to $300 million.