Radványi was born into a Jewish family in Hungary. As a boy, Radványi attended a grammar school on Marko Street in Budapest. While attending grammar school, at the age of 16, he authored a book of poetry, which received a preface from Frigyes Karinthy. Radványi studied economics and philosophy at the University of Budapest from 1918 to 1919, where he became involved in radical politics. With the destruction of the Hungarian Soviet Republic in 1919 he fled to Vienna, where he adopted the pseudonym "Johann :de:Lorenz Schmidt|Lorenz Schmidt", from the 18th-century Protestant dissident theologian. Radványi studied philosophy in Germany at Heidelberg University, where he obtained his doctorate in 1923. Directed by Karl Jaspers, his thesis on Chiliasm was 'summa cum laude'. While at Heidelberg, Radványi met the poet Anna Seghers. They married in 1925 and had two children, :de:Pierre Radványi|Pierre and Ruth.
After finishing their studies at Heidelberg, Radvanyi and Seghers moved to Berlin, where Radvanyi directed the Marxistische Arbeiterschule from 1925 to 1933. Radványi gathered faculty members such as Georg Lukács and Bertolt Brecht, and speakers such as Albert Einstein, who in 1931 hosted a conference titled "What a worker must know about the Theory of Relativity". László indicated in his letters in 1926 the impossibility of obtaining a job as a philosophy professor in Germany because of his "Hungarian-ness and Jewishness". The German government closed the Marxistische Arbeiterschule in 1933, and Radványi then left for Paris. In Paris, Radványi founded and directed the Freie Deutsche Hochschule, however, the German invasion of Paris forced Radványi to abandon his new endeavour. In 1940, the police in Meudon detained him as a citizen of a country allied with Germany. In December 1940, Seghers obtained a visa for herself, her husband, and their children with the help of Karl Mannheim. The family did not leave France until March 24, 1941, after they had received a transit visa from the United States; they arrived in New York on June 16, 1941. They departed June 25, 1941, aboard the SS Monterrey. The SS Monterey's manifest of passengers also included the French anthropologist Claude Lévi-Strauss and surrealistic writer André Breton for New York City and the port of Veracruz, in the Gulf of Mexico.
Der Chiliasmus: ein Versuch zur Erkenntnis der chiliastischen Idee und des chiliastischen Handelns. Budapest: Lukács Archívum 1985. Dissertation Heidelberg 1923.
Probleme des Neokolonialismus: die Besonderheiten des westdeutschen Neokolonialismus. Berlin: Akademie-Verlag 1963.
Die Entwicklungsländer: Ursprung, Lage, Perspektive. Berlin: Verlag Die Wirtschaft 1974.
Internationale Konzerne. Berlin: Verlag Die Wirtschaft 1981.
Probleme des kapitalistischen Weltmarktes. Herausgeber: J. L. Schmidt, K. H. Domdey. 1958