Among his most significant works was the 1924 book Les Paysans du Nord pendant la Révolution française ("The Peasants of the North During the French Revolution"), which was the result of 20 years of research into the role of the peasantry during the revolutionary period.
Lefebvre began writing in 1904, but it was not until 1924, at the age of fifty, that he was finally at the point in his career - no longer preoccupied with supporting his family - that he was able to finish his doctoral thesis: Les Paysans du Nord pendant la Révolution française.
Lefebvre's work on this thesis was "based on a thorough analysis of thousands of tax rolls, notarial records, and the registers of rural municipalities, whose materials he used to trace the effects of the abolition of feudalism and ecclesiastical tithes, the consequences of property transfers, the movement of the bourgeoisie onto the countryside, and the destruction of collective rights in the peasants villages".
The Vichy régime suppressed the book, ordering 8,000 copies to be burned; as a result the work was virtually unknown in its native land until it was reprinted in 1970.
Its reputation was already secure in the English-speaking world, however, since the English translation, The Coming of the French Revolution (1939) had established it as a clear, yet subtle, classic.
In 1935 Georges Lefebvre became the president of the Societé des Études Robespierristes and the director of the Annales historiques de la Révolution française.