The ship La Amistad becomes the setting for a harrowing tale of rebellion and struggle as it carries Africans captured from Sierra Leone and sold into slavery in Cuba. One of these captives, Sengbe Pieh, known by his slave name Cinque, bravely leads a revolt aboard the vessel, resulting in the death of most of the crew. The remaining crew members, kept alive by the Africans' hope of navigation, are believed to guide the ship back to West Africa.
Weeks pass, and the ship runs dangerously low on provisions when land finally comes into view. To fetch fresh water, a group ventures to shore, unaware that a United States military vessel is waiting nearby. The Spaniards deceitfully navigate the ship up the Atlantic coast, leading to La Amistad being seized and the Africans imprisoned while the court deliberates ownership and the fate of the slaves. Although Great Britain, the United States, and Spain have outlawed the international slave trade, the Spanish claim the Africans were birthed on a Cuban plantation, making them legal domestic slaves.
In Washington, D.C., former President John Quincy Adams, now a member of the U.S. House of Representatives, aligns himself with prominent abolitionists, including Theodore Joadson, a freed slave, and activist Lewis Tappan. United in their pursuit to secure the freedom of the Africans on Amistad, they plead for Adams' legal expertise, though he remains ambivalent towards slavery itself. Amidst this turmoil, President Van Buren faces pressure from Spanish Queen Isabella II, who demands payment for the vessel and its human cargo.
The Africans are charged with "insurrection on the high seas," while conflicting ownership claims arise—from Spain, the U.S., the Spanish owners of the Amistad, and the captain of the U.S. vessel that seized it. Seeking legal help, the abolitionists turn to Roger Sherman Baldwin (Matthew McConaughey), a property law expert. Alongside linguist Josiah Willard Gibbs, Sr., they struggle to communicate with the Africans, trapped in a silence borne from language barriers.
During a conversation with the abolitionists, Baldwin turns to Adams for guidance, who asserts that the side with the most compelling narrative typically prevails in court. Realizing their need to communicate effectively with the Africans, they find a Royal Navy sailor, James Covey, who speaks an African dialect. As a translator, Covey helps Baldwin and his team understand Cinque's heart-wrenching account—how he was seized, enslaved, and finally sold at a slave market in Cuba.
Despite these revelations, the District Attorney [William S. Holabird] and Secretary of State [John Forsyth] dismiss Cinque's powerful testimony as mere fiction. In a twist of fate, Baldwin discovers a notebook aboard La Amistad, which documents the illegal slave trading activities. Presenting this evidence, he enlists expert testimonies, including that of Captain Fitzgerald, a British officer committed to enforcing anti-slavery policies in West Africa. Ultimately, Judge Coglin orders the arrest of the owners of La Amistad and facilitates the opportunity for the Africans to return home.
Tensions rise further when Senator [John C. Calhoun] confronts President Van Buren, highlighting the economic significance of slavery in the South and warning of impending conflict should the Africans be freed. Under immense pressure, Van Buren appeals the case to the U.S. Supreme Court, comprised predominantly of Southern slave-holding justices.
With pivotal moments unfolding, Joadson and Baldwin share the troubling news with Cinque, leading to a necessary re-engagement with Adams. Following a heartfelt conversation at Adams' residence, he pledges his support for the cause. In the Supreme Court, Adams makes a heartfelt appeal on behalf of the Africans, leading to their eventual release and the option to return to Africa if they choose. As a poignant farewell, Cinque parts ways with his American allies.
In a parallel story, British Royal Marines attack the Lomboko Slave Fortress, liberating those imprisoned within. With the fortress reduced to ruins, Captain Fitzgerald oversees its destruction. Meanwhile, Van Buren’s political aspirations falter as he loses his reelection bid. As Cinque and his fellow captives sail back to Sierra Leone with Covey, they confront the tragic reality of civil unrest in their homeland, with Cinque's family lost and likely sold into slavery.
