Clarkson and his abolitionist friends knew that for their movement to be successful, they needed to gain the support of Members of Parliament who could help them legalize the abolition of the slave trade, and eventually the abolition of slavery. Many abolitionists were Quakers, who were forbidden from sitting in Parliament, but there were a few Members of Parliament who were Anglicans, another religious group that was involved in the movement. If the abolitionists could gain the support of these Anglican Members of Parliament, they would have a way to get abolition legalized.
In May 1787, Clarkson and his colleagues founded the Committee for the Abolition of the Slave Trade, a group of abolitionists whose goal was to convince MPs to support abolition bills in Parliament. During this time, Clarkson met William Wilberforce, an Anglican MP with whom Clarkson would work closely with for the rest of his life.
Clarkson became the leading researcher of the Committee, gathering evidence to support abolition bills in Parliament and gain followers for the movement. This role was often a dangerous one, as many slave traders and captains of slave ships didn’t like Clarkson hanging around the slave ports and asking too many questions. The slave trade made a lot of men a lot of money, and abolitionists weren’t liked in these places. On one occasion, on a visit to Liverpool, one of the busiest centers of business for the slave trade, he was attacked and nearly killed by a group of sailors.
Clarkson was often influential on his travels. On a visit to Manchester in October 1787, he gave a rousing speech on abolition, and that influenced the growth of the movement in that city. Clarkson traveled around England, visiting the major ports of the country for the next two years. He interviewed thousands of sailors and doctors who worked on slave ships, who were more than willing to share the horrible conditions that existed aboard slave ships. Two doctors, in particular, James Arnold and Alexander Falconbridge, worked closely with Clarkson, detailing their experiences as ship surgeons and allowing him to publish their experiences.
Clarkson was particularly famous for his “box” of evidence. Over the course of his travels, he kept the visual evidence he collected in a box and would pull it out at meetings and speeches. The box included materials and instruments used to torture slaves on the ships and examples of African goods. He used this box to prove how brutal the trade was and how detailed and sophisticated the African goods were. He realized that this had more of an effect on convincing people to support abolition than his speeches did, and he used it to move people to support his cause.
Clarkson’s working partnership with William Wilberforce in the abolitionist movement was legendary. The two men worked together for their entire lives to eradicate the slave trade and slavery. Clarkson was the hands and feet of the movement, constantly traveling and collecting evidence. Wilberforce was the public face, using Clarkson’s work and research as ammunition for his yearly abolition bills that he brought before Parliament.
Clarkson’s writings and publications became influential and provided much of the support for the abolition bills in Parliament, one of which was the famous Brookes’ Diagram, which was a diagram showing how many slaves were packed on a slave ship.
Clarkson and Wilberforce worked with the members of the Committee for the Abolition of the Slave Trade to create a movement from the ground up, convincing the public to support the abolition movement through speeches and visits around the country. Despite the public support, Parliament wouldn’t pass the abolition bill. After all of his hard work, Clarkson suffered from exhaustion and retired to the country. England went to war with France, which halted the abolition campaign. Clarkson retired from the campaign for ten years, during which he married and settled in southern England.
By 1804, the war with France was ending, so Clarkson, Wilberforce, and their fellow abolitionists renewed their cause. After his long sabbatical, Clarkson got back on his horse and began traveling again, going from city to city, collecting more evidence and testimony. This time, they couldn’t fail. In 1807, the Abolition of the Slave Trade Act finally passed through Parliament. It eliminated the slave trade throughout the British Empire. Clarkson had spent most of his adult life campaigning for the end of the British slave trade, and now it was over.
Now that the slave trade was abolished, he turned his attention to eliminating the slave trade in other countries and ending slavery once and for all. The French and Spanish continued to trade in slaves, and Clarkson became an active campaigner abroad to end the trade, traveling to France on more than one occasion to support the end of the trade and the end of slavery.