One of the most heroic figures in the Amistad affair was neither African nor American, but an Irish Catholic named Richard Madden. Madden was a man of culture, fluent in several languages, an author and poet, former judge, and one of the period's most zealous opponents of slavery. Madden's crusade to end slavery had taken him from the ports of West Africa to the infamous barracoons (slave markets) of Havana to the offices of world leaders. His efforts to persuade leaders to more actively work to eliminate slavery usually were met with disdain, indifference, and even (as from President Andrew Jackson) laughter.

Madden was the head of the British Anti-Slavery (or Mixed) Commission in Havana, a body charged with enforcing the provisions of the 1820 British-Spanish treaty banning the importation and trade of slaves. In this post, Madden came to understand the slave trade in Cuba, from the nighttime landings of Portuguese slave ships in Havana Harbor to the use of fraudulent documents and passports to hide the slaves' origins.  Cuban officials resented Madden's efforts to stem the illegal trade in slaves and American officials on the island were equally unhelpful. Except in rare cases where British vessels were able to intercept slave traders on the high seas, the trade of slaves in Cuba continued unabated to the time of the Amistad incident.

Madden read a newspaper account of the Amistad's landing in the United States and knew well the likely fate of the Africans should they be returned to Cuba for trial. Madden hopped a molasses-carrying cargo ship and sailed to New York to see what he could do to help. Upon arrival, Madden sought out Lewis Tappan who asked Madden if he would testify at the upcoming district court trial in Connecticut. He said that of course he would be willing. In November of 1840 Madden, together with Baldwin and Tappan, boarded a carriage in New Haven for a journey to the courthouse in Hartford. One can only imagine how the provincial minds of Tappan and Baldwin must have been stimulated by the vastly more worldly Madden.

After the first few witnesses were called in Hartford, the trial was postponed until January because of the illness of the attorney for Meade and Gedney. Madden was, however, nonetheless allowed to offer a deposition which was introduced as evidence in the January trial. In his deposition, Madden described the nature of the slave trade in Cuba and confirmed the recent arrival from Africa of the captives. He described a September visit to the barracoon where the Amistads were sold, and how the operator of the barracoon regretted the loss of so many fine slaves, who he assumed would surely be executed in the United States.

After giving his deposition in Hartford, Madden returned to England where he briefed Queen Victoria on the Amistad incident.