Theweleit was born in Ebenrode, East Prussia (now Nesterov, Russia), the son of a railway company worker. He wrote the following about his father: "Above all he was a railroader, wholeheartedly, as he used to say, and then a human being. He was a rather good human being and a good fascist. His beatings which he gave away abundantly and brutally as it was usual in his time and with the best of intentions were the first lessons I received on fascism, a fact I only later fully discovered."
Theweleit studied German studies and English studies in Kiel and Freiburg. From 1969–1972, he worked as a freelancer for a public radio station (Südwestfunk).
He wrote his dissertation Freikorpsliteratur und der Körper des soldatischen Mannesabout Freikorps narratives, a sub-literature produced by pre-fascist paramilitaries organized in Freikorps, who, during the early Weimar republic, had fought external or internal enemies. In academia only few historians had read and analysed this literature before Theweleit. His book Männerphantasien (1977); translated as Male Fantasies (1987), a study of the proto-fascist consciousness in general and the bodily experience of these former soldiers in particular, was well received and much discussed. Throughout the book Theweleit uses ideas, terminology and empirical experience from works of Margaret Mahler, Wilhelm Reich, Gilles Deleuze, Félix Guattari, Melanie Klein, and Michel Foucault among others to develop his theory of the fascist male imprinting and socialization. In the introduction Theweleit points out that discussions with Margaret Berger and his wife Monika Theweleit-Kubale (both have professional clinical experience) did have an important influence on the book as well as the feedback from Erhard Lucas a leading German left-wing historian of the Weimar Unrest.
Theweleit writes in a non-orthodox, highly personal and associative style. His book are heavily illustrated with cartoons, advertisements, engravings, posters and artwork.
Theweleit lives in Freiburg, he teaches in Germany, the United States, Switzerland, and Austria. He was a lecturer at the Institute of Sociology at the University of Freiburg and lecturer at the film academy in Berlin. From 1998 until retirement he was a professor for "art and theory" at the Staatlichen Akademie für Bildende Künste, the art college, at Karlsruhe.