Abstract Every empire in the Americas developed a law of slavery that connected the forced transoceanic migration of enslaved people with land-based economic production and social life. Competing conceptions of jurisdiction over land and sea emerged from legal processes regarding slavery in the transition from colonial Portuguese rule to early independence in Brazil. Both the Portuguese monarch and post-independence Brazilian ministers sought to assert jurisdiction over residents inside the territory, including enslaved people. Their attempts to do so created social conflicts in which enslaved people put forth their own visions of jurisdiction and justice. Afro-Brazilian people developed a legal politics that drew upon diasporic maritime connections to overturn enslavement. The legal politics of cases regarding uprisings and contraband slave-trading animated concerns among judges and imperial administrators about effective legal order. A revolutionary movement in 1798 contested Portuguese colonial sovereignty with a vision of free-trade popular sovereignty. The monarch’s transfer from Portugal to Brazil in 1808 opened a small route for enslaved people to petition the crown for freedom based on innovative readings of free soil. A major case of capture in 1851 illuminated how the naval court judge adjudicated the case as the capture of an enemy. Captive African people testified in court to gain collective freedom in a liminal space. These claims to freedom raised important questions about legal equality and freedom from illegal trafficking for all people held in slavery in Brazil.