His book World in Trance (1943) is a history of international relations during the interwar years. A review in Foreign Affairs called it an "attempt to reinterpret the history of the two inter-war decades in terms of the progressive disintegration of Allied resistance to Germany's military revival". It was praised by Winston Churchill but criticised by H.G. Wells, who called Schwarzschild "superficially intelligent and massively stupid", and Michael Foot, who denounced it as "a facile, scintillating treatise which...has received applause from those weary brains which prefer the dismal past to the adventurous future". A. J. P. Taylor called the book a "brilliant argument in favour of firmness".
In the first edition of his The Open Society and Its Enemies (1945), Karl Popper distinguished between Karl Marx himself and his followers, claiming that they had transformed Marx's works into an unscientific dogma. However, Popper added a note to the fifth edition: "Some years after I wrote this...Leopold Schwarzschild's...The Red Prussian...became known to me...it contains documentary evidence, especially from the Marx-Engels correspondence, which shows that Marx was less of a humanitarian, and less of a lover of freedom, than he is made to appear in my book. Schwarzschild describes him as a man who saw in 'the proletariat' mainly an instrument of his own personal ambition. Though this may put the matter more harshly than the evidence warrants, it must be admitted that the evidence itself is shattering".
- End to Illusion: A Study of Postwar Europe (1934).
- World in Trance (1943).
- Primer of the Coming World (1944).
- Karl Marx: The Red Prussian, The Universal Library, Grosset & Dunlap (1947).
- The Red Prussian: The Life and Legend of Karl Marx (1948; 2nd ed. 1986).
- Chronicle of a Downfall: Germany, 1929-1939 (2010).
- Schwarzschild, Leopold (1943). World in trance. Hamish Hamilton. ASIN B0007IX5O8.
- Robert Gale Woolbert, 'Recent Books on International Relations', Foreign Affairs Vol. 21, No. 3 (Apr., 1943), p. 574.
- "INTERNATIONAL: The Old Adam" (abstract). Time. 24 July 1944. Retrieved 12 March 2013.
- A.J.P. Taylor, The Origins of the Second World War (London: Penguin, 1991), p. 344.
- Leopold Schwarzschild, The Red Prussian: The Life and Legend of Karl Marx (London: Pickwick Books, 1986), p. 4.