The Anti-Slavery Society was the everyday name of two different British organisations.
The first was founded in 1823 and was committed to the abolition of slavery in the British Empire. Its official name was the Society for the Mitigation and Gradual Abolition of Slavery Throughout the British Dominions. This objective was substantially achieved in 1838 under the terms of the Slavery Abolition Act 1833.
The elimination of slavery throughout the world was frequently in the mind of early abolitionists. The Committee for the Abolition of the Slave Trade, which established the Society for the Abolition of the Slave Trade in Britain in 1787, campaigned for an end to the Transatlantic slave trade from Western Africa to the New World, which Britain dominated by then.
The Slave Trade Act 1807 made the slave trade illegal in the British Empire. Following this, British abolitionists turned their attention to abolishing slavery itself, first in British colonies, and later in the US and the colonies of other European powers (e.g., in South America), and in parts of the world where it had long been legal, such as in the Middle East, Africa, and China.
The first British organisation to refer to itself as the Anti-Slavery Society was founded in Britain in 1823. Founding members included William Wilberforce and Thomas Clarkson. Its official name was the Society for the Mitigation and Gradual Abolition of Slavery Throughout the British Dominions.
Its work included supporting the first account of slavery to be published by a Black woman, Mary Prince, The History of Mary Prince, A West Indian Slave (1831). The publishers were sued by the family from which she had escaped. The book was much sought after, running into three editions in the year of its publication.