This article analyzes the ways that discussions regarding the abolition of the slave trade held at the Congress of Vienna (1814–1815) affected slavery in the Iberian empires. Drawing from newspaper coverage, diplomatic correspondence, and conference minutes, we reassess the conditions under which Portuguese and Spanish agents negotiated with their British counterparts; highlight the Iberian political dilemmas that surfaced at the Congress; and elucidate the plenipotentiaries’ subsequent resolutions addressing the transatlantic slave trade. As a result of the talks held in Vienna, Spanish subjects in Cuba and Portuguese subjects in Brazil established political and diplomatic strategies to support slavery in order to maintain their positions in the world market of tropical goods. In other words, while slavery was undergoing reconfiguration in Brazil and Cuba, slave-owners and their political representatives were forced to engage with the hegemonic, abolitionist discourse systematically established by the British at the Congress in order to formulate their proslavery response. The article thus demonstrates that the Congress of Vienna was integral to the international consolidation of the politics of “second slavery” in the Americas. In other words, Brazil and Cuba were forced to engage with the hegemonic discourse systematically established by the British at the Congress in reconfiguring slavery and formulating their proslavery defense.