“God Almighty has set before me two great objects, the suppression of the Slave Trade and the Reformation of Manners.”
William Wilberforce, Journal
(in case you’re wondering, ‘manners’ was a way of speaking about morals, not which fork to use for the entree)
Wilberforce’s great inclination after being found by God, was to abandon politics and enter into ministry with the Church. He talked this desire over with John Newton, the leading evangelical preacher in London, who advised him to remain in the Parliament and to use his position there to serve God.
Wilberforce also talked with it over with William Pitt, the Prime Minister urged him to remain with him in the House. 
Wilberforce’s ability as a Parliamentary debater was deeply important for Pitt. Wilberforce was acknowledge to be the best speaker in the house and his reduction to ridicule of opponents of Pitt’s policies was significant at a time when party divisions were still very fluid.
It was during this time that Wilberforce was introduced to the Abolitionist Movement through Sir Charles Middleton. It was this cause that really hooked William into remaining in Parliament throughout the rest of his life. Newton used the Abolitionist cause to help Wilberforce see the way in which he could serve God through politics; Pitt used it to offer Wilberforce a carrot to keep him at his side.
Whatever the reason, Wilberforce spent 44 years in Parliament, time which was dominated by his advocacy of the abolition of the Slave trade.
Mind you, this was at a time when politics really was interesting. We’re not talking individual workplace agreements versus collective bargaining. Good grief no!
This is the age of the French Revolution, the Napoleonic Wars, the Madness of King George, and most of the population permanently drunk as skunks on cheap Gin.
And, as a historical footnote Australia became the worlds largest prison Island.
The causes for which Wilberforce advocated make interesting reading. Obviously, there was his opposition to the Slave Trade, but before you adopt our William as the patron saint of bleeding-heart liberalism, it’s worth knowing that his attitude towards the working class in Britain would make him deeply unpopular among the Comrades.
Most of the leaders of Britain got a little bit edgy around the time of the French Revolution. There was a general suspicion (probably not unfounded) that the local proles might like to try the blade of ‘Liberty, Egality, Fraternity’ out on some English necks. Wilberforce opposed the extension of the right to vote to the working classes and led the establishment of the Society for Suppression of Vice and Encouragement of Religion to curb political aspiration and support for the French Revolution (by locking up people or sending them to Australia).
Back on the nice side of the ledger, Wilberforce was one of the founding members of the Church Missionary Society (CMS) and the Society for the Prevention of Cruelty to Animals (now the RSPCA). He had a strong interest in the provision of chaplains and missionaries in British colonies around the world. He worked hard to ensure that the Charter of the British East India Company included the requirement that the Company employ people to share the Christian message with people in India (this was deeply unpopular with the Directors of the Company). Also over opposition, he arranged for a chaplain to be sent with the First Fleet of Convict ships – sent to establish a colony in Australia. That Chaplain was Richard Johnson, who was a committed evangelical Christian and who must have been extremely brave to take the job.
On the 12 May 1789 Wilberforce stood to make his first major speech on the subject of Abolition in the House of Commons. The speech drew heavily on work done by Thomas Clarkson in gathering evidence of the appalling conditions in which Slaves were carried through the Middle Passage – the journey from Africa to the West Indies. Clarkson, Wilberforce, and others of the Abolitionist movement ran one of the first great grass-roots political campaigns. Clarkson travelled with his evidence and stories, holding public meeting to gather support. Pamphlets were printed and even little supporters buttons were made.
The Punters were all for it, but the King was strongly against, and there was a belief in the Parliament that abolition of the slave trade would lead to economic ruin.
In April 1791, Wilberforce introduced the first Parliamentary Bill to abolish the slave trade, which was easily defeated by 163 votes to 88.
This began one of the most determined and protracted Parliamentary battles ever seen. In every subsequent session of Parliament from that year through to 1807, Wilberforce introduced his motion to abolish the Slave Trade. They’d knock him down and he’d get right back up again.
Things might have been considerably smoother if there hadn’t been a raging war with France. For most people (other than Africans rotting in stinking ships) the abolition of Slavery wasn’t top of the shopping list.
However, the mood began to change during the first years of the 19th Century.
The Abolitionists got smarter as well, in 1806 they introduced a bill that legally allowed British Privateers (Pirates) to hijack any ships involved in the slave trade who were flying an American flag. The legislation was couched in terms that suggested its intent was to cripple the French Colonies in the Americas, and do the nasty and newly independant Americans a bit of harm as well. The plan was dreamed up by maritime lawyer James Stephen who knew full well that the vast majority of British Slave Ships were flying the American Flag once they left British waters in order to avoid trouble with the French and Americans at the other end. The Abolitionists organised the Bill to be presented by an MP who was not associated with their cause, and to do it at a time when the majority of MPs were out of the House. The Foreign Slave Trade Act sailed through on smooth waters.
And by doing so, they had managed to effectively prohibite two-thirds of the British slave trade.
“… cunning as serpents, innocent as doves.”
From that point on the tide was with the Abolitionist Movement. The following year (1807), knowing that the King had withdrawn his opposition, the Bill was reintroduced into the House of Commons and was carried by 283 votes to 16. The whole House rose to their feet and cheered and applauded Wilberforce. And William, who had carried on the fight for 20 years, sat there and wept.
The King signed the Bill into law on the 25 March, 1807.