Werner Maser was best known for his 1971 study of Hitler, Adolf Hitler: Legende, Mythos, Wirklichkeit ("Hitler: legend, myth and reality"), which was translated into over 20 languages (and published in English as Hitler, 1973), a great achievement considering the vast literature on the subject. The volume was just part of a long study of the Third Reich which included not only the Nazi leader, but also his party, the Nuremberg trials, German-Soviet relations and much more.

He had published on the early history of the Nazi party in 1965, and on Hitler's Mein Kampf in the following year. His Hitlers Briefe und Notizen Sein Weltbild in handschriftlichen Dokumenten (1973; translated as Hitler's Letters and Notes, 1974) provided insight into Hitler's thoughts and theories. Adolf Hitler: das Ende der Führer-Legende ("The End of the Führer Legend") appeared in 1980. Maser also tracked down Hitler's medical records from 1905 to 1945, which for decades had been presumed lost.

More controversial was Nürnberg: Tribunal der Sieger 1977, translated as Nuremberg: a nation on trial, 1979). Fritz Stern described it as "a significant work, based on the proceedings of the International Military Tribunal and on additional extensive inquiries, which recall - among other things - the many pleas of ignorance and innocence".

He was the first historian to recognise that purported diaries of Hitler, which were published by Stern magazine in 1983 and authenticated by Hugh Trevor-Roper, were forgeries.