The first anti-slavery statement was written by Dutch and German Quakers, who met at Germantown, Pennsylvania in 1688. English Quakers began to express their official disapproval of the slave trade in 1727 and promote reforms. From the 1750s, a number of Quakers in Britain's American colonies also began to oppose slavery, and called on English Quakers to take action with parliament. They encouraged their fellow citizens, including Quaker slave owners, to improve conditions for slaves, educate their slaves in Christianity, reading and writing, and gradually emancipate (free) them.
An informal group of six Quakers pioneered the British abolitionist movement in 1783 when the London Society of Friends' yearly meeting presented its petition against the slave trade to Parliament, signed by over 300 Quakers. They were also influenced by publicity that year about the Zong massacre, as the ship owners were litigating a claim for insurance against losses due to more than 132 slaves having been killed on their ship.
The Quakers decided to form a small, committed, non-denominational group so as to gain greater Church of England and Parliamentary support. The new, non-denominational committee formed in 1787 had nine Quaker members and three Anglicans. As Quakers were not prepared to receive the sacrament of the Lord's Supper according to the rites of the Church of England, they were not permitted to serve as Members of Parliament, having Anglican members strengthened the committee's likelihood of influencing Parliament.
Nine of the twelve founding members of the Society for Effecting the Abolition of the Slave Trade were Quakers: John Barton (1755–1789); William Dillwyn (1743–1824); George Harrison (1747–1827); Samuel Hoare Jr (1751–1825); Joseph Hooper (1732–1789); John Lloyd;
Joseph Woods Sr (1738–1812); James Phillips (1745–1799); and Richard Phillips. Five of the Quakers had been amongst the informal group of six Quakers who had pioneered the movement in 1783, when the first petition against the slave trade was presented to Parliament.
Three Anglicans were founding members: Thomas Clarkson, campaigner and author of an influential essay against the slave trade; Granville Sharp who, as a lawyer, had long been involved in the support and prosecution of cases on behalf of enslaved Africans; and Philip Sansom.