William IV was the British monarch on the throne when the Slavery Abolition Act was passed in 1833. He gave royal assent to the Act on 28 August 1833, during the reforming ministry of Prime Minister Charles Grey.
The legislation abolished slavery across most of the British Empire, although it did not take effect immediately. Its main provisions began on 1 August 1834. Many enslaved people over the age of six were initially classified as “apprentices,” forcing them to continue working for former owners; this system was finally ended in 1838 in most colonies.
The Act followed decades of campaigning by abolitionists including William Wilberforce and Thomas Clarkson. It also differed from the Slave Trade Act of 1807, which outlawed Britain’s participation in the transatlantic slave trade but did not abolish slavery itself. India and some other territories were excluded from the 1833 legislation, so emancipation across the British imperial system happened unevenly.