Lassalle passed his university examinations with distinction in 1845 and thereafter traveled to Paris to write a book on Heraclitus.
Lassalle was a committed republican from an early age and during the German Revolutions of 1848 he spoke at public meetings for the revolutionary-democratic cause and urged the citizens of Düsseldorf to prepare themselves for armed resistance to the November decision of the Prussian government to dissolve the National Assembly.