Shortly after his first speech in Parliament against the slave trade in 1789, Wilberforce moved to Clapham, to live with Thornton, his cousin, in a house on the west side of the Common.
Whilst many people outside the area joined the cause, Clapham and Holy Trinity remained the heart of the campaign right up until 1833, when Parliament finally passed the Slavery Abolition Act as Wilberforce lay on his deathbed. By the end of 1838, slavery in the British Empire had ended, and it was largely thanks to the work of the members of the Clapham Sect.
The church itself was built in 1776, the same year as the American Declaration of Independence, and subsequently underwent some adaptations inside to fit changing congregations. During the Second World War it suffered serious damage and the main roof was close to collapse as a result. Restoration was completed by 1952, and the church remains in use today.
For more on the Clapham Sect see the Holy Trinity Clapham website.