This paper argues that to liberal authoritarianism – defined here as a liberal technique of government fusing authoritarianism with liberalism for the purpose of the ‘free market’, following Hermann Heller – corresponds a form of dual constitutionalism or fragmented legality. Dual constitutionalism, originally a colonial technique of governance, relies on a liberal constitution enshrining a state of exception which suspends it on specific matters, territories, and during certain times. It can be either military – called in France the ‘state of siege’, the continental version of the British Martial Law – or civilian – the ‘state of emergency’. In the case of France, liberal authoritarianism has witnessed several declinations since the French Revolution, flourishing in the liberal colonialism of the late 19th century, then the full-fledged liberal authoritarianism of the interwar period, and eventually in the neoliberal authoritarianism of the 4th and 5th republic. Focusing on the relationship between France and its Algerian colony during the Third Republic (1870–1940), one of the most liberal periods ever in French history, it documents how the State of Exception was used to establish a legalised state of dictatorship where all executive, legislative and judicial powers were vested in the hands of a governor, in order to force the creation of markets by breaking down collective land ownership and use and other non-liberal economic customs of the local population, using, in particular, the legal tool of the ‘sequestre’ which allowed the State to forcibly expropriate land and seize assets of the local population without compensation, forced labour and internment camps – all in order to incentivise ‘free enterprise’ by the colonisers. Many of these legal tools and techniques migrated back to the metropolis when the Third Republic officially dissolved into a Nazi State in 1940, through legal means and in accordance with the constitutional procedures of the Third Republic.