After taking his Abitur in 1937, he spent time in Italy, where he wrote his first book, Tage und Nächte steigen aus dem Strom.

As a Leutnant zur See in the autumn of 1941, Buchheim joined Kapitänleutnant Heinrich Lehmann-Willenbrock and the crew of U-96 on her seventh patrol in the Battle of the Atlantic.

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).

Through the 1950s and 1960s, he established an art publishing house, and he wrote books on Georges Braque, Max Beckmann, Otto Mueller and Pablo Picasso.

He collected works by French and German Expressionist artists, from groups including Die Brücke and Der Blaue Reiter, such as Ernst Ludwig Kirchner, Max Pechstein, Emil Nolde, Wassily Kandinsky, Paul Klee, Franz Marc, Gabriele Münter, Alexej von Jawlensky, and Max Beckmann.

[3] In 1973 he published a novel based on his wartime experiences, Das Boot [de] (The Boat), a fictionalised autobiographical account narrated by a "Leutnant Werner".

He subsequently also wrote the autobiographical novels Die Festung (The Fortress, 1995), a sequel to Das Boot based on his travels home across France in 1944, and Der Abschied (The Parting, 2000), about the nuclear-powered cargo vessel NS Otto Hahn.

In June 2000, the Sprengel Museum in Hanover voted to return a Lovis Corinth’s painting, “Walchensee, Johannisnacht” (“The Walchensee on St John’s eve”) which its donor, Dr. Bernhard Sprengel, had purchased from Buchheim, to the heirs of Dr Gustav Kirstein and his wife Therese Clara Stein, who committed suicide due to Nazi persecution.

[7] Buchheim married Geneviève "Gwen" Militon, a resistance fighter from Britanny who appears in his novels as Simone Sagot, and whom he also painted.

He used a camping table in his dining room, and according to his son, did not pay taxes and reused print blocks made by Otto Müller, forging the artist's initials.