The Defensor de Pedro did not begin its voyage as a pirate ship. Its first captain, an officer of the Imperial Navy of Brazil called Mariz de Sousa Sarmento, maintained a reliable and steady reputation in the Atlantic seafaring community. In 1827, Captain Sarmento obtained a legitimate commission from Dom Pedro I, the Emperor of Brazil, to trade in slaves and take prizes. He intended to sail from Rio de Janeiro in November. Unfortunately for Captain Sarmento, this was a very precarious and volatile time to be slave-trading and prize-taking on the Atlantic Ocean.

Dom Pedro was the son of the Portuguese king Dom Juan VI. To defend Portuguese colonial interests from Napoleon's advances during the Revolutionary Wars, Dom Juan sent Pedro to Brazil. As Spanish American colonies began agitating for independence after the war, Dom Pedro pushed for Brazilian independence. He authorised Brazilian privateering against Portuguese ships until his father granted Brazil independence from Portugal in 1822. The new Empire of Brazil occupied a huge geographic area and contained a multitude of provinces with competing loyalties and interests. During a visit in 1821, Captain Richard Fox wrote, ‘I observed people to have but little confidence in each other; doubts and mistrust appeared to be the ruling passions, and even in almost every family there appeared to be a division of political sentiments.’ In general, the north held more allegiance to Portugal through the retention of Portuguese military assets and trade ties, while the central south held the true believers in independence in Rio de Janeiro, São Paulo and Minas Gerais. This volatile domestic environment persisted and began to complicate Dom Pedro's efforts for international recognition of Brazilian sovereignty.

The first danger for Captain Sarmento was the component of his commission that authorised a shipment of slaves. Brazil's wealthy and influential landowners relied heavily upon slaves to run its lucrative agricultural sector. The deplorable conditions of the slaves’ day-to-day lives, assuming they survived their initial Atlantic crossing, drove a constant need to replenish slave labour. However, a burgeoning anti-slavery movement had already spread across the Atlantic. By 1827, obtaining new slaves from Africa was complicated by the British Royal Navy's active intervention against foreign ships carrying slave cargoes.