This article reads the work of Luiz Gama (1830-1882), the Brazilian abolitionist, former slave, and self-taught lawyer, as both theorizing and enacting a politics of institutional prefiguration. Against oligarchic domination by slave-owning elites and the monarchical rule of the Brazilian Emperor, Gama defended a radical republican vision of the law: the 'right of revolution' (direito de revolução), which he saw as already being practiced in acts of resistance. Repurposing the legal pluralism of Friedrich Carl von Savigny for emancipatory politics, Gama's provocationhis insurgent legality -consisted in envisioning the resistance of the enslaved as an inaugural site for a republican order in the making. More than strategically mobilizing law in freedom suits, Gama presented the self-organization of maroons as both defending usurped rights, inherited from Roman law, and laying the foundations of an emergent republic. Drawing on broader currents of plebeian republicanism in the Atlantic world, he conceptualized the resistance of the enslaved as a 'civic virtue.' Gama's insurgent legality thereby recasts the relation between prefigurative politics and institutional forms, questioning dichotomies of resistance and order, rupture and durability. Beyond nineteenth-century Brazil, Gama's institutional thought speaks to debates in contemporary radical democratic and republican theory.