In 1797, William Wilberforce is severely ill and taking a recuperative holiday in Bath, Somerset, with his cousin, Henry Thornton. It is here that Wilberforce is introduced to his future wife, Barbara Spooner. Although he initially resists any romantic overtures, she convinces him to relate the story of his career.
The story flashes back 15 years to 1782, and Wilberforce recounts the events that led him to where he is now. Beginning as a young, ambitious, and popular Member of Parliament (MP), he experiences a religious enlightenment and aligns himself with the evangelical wing of the Church of England. Wilberforce contemplates leaving politics to study theology, but is persuaded by his friends William Pitt, Thomas Clarkson, Hannah More, and Olaudah Equiano that he will be more effective doing the work of God by taking on the unpopular and dangerous issue of the abolition of the British slave trade. His conviction in the cause deepens following a meeting with his former mentor John Newton (introduced mopping a church floor dressed in sackcloth) who is said to live "in the company of 20,000 ghosts… slaves". As a former slave ship captain turned Christian, he deeply regrets his past life and the effects on his fellow man. Newton urges Wilberforce to take up the cause.
Pitt becomes Prime Minister and Wilberforce becomes a key supporter and confidant. Pitt gives Wilberforce the opportunity to present a bill before the house outlawing the slave trade. Wilberforce's passionate campaigning leads him to become highly unpopular in the House of Commons. He is opposed by a coalition of MPs and peers representing vested interests of the slave trade in London, Bristol, Glasgow, and Liverpool led by Banastre Tarleton and the Duke of Clarence. Despite popular support and the assistance of an unlikely ally in the form of Charles James Fox, Wilberforce's bill to abolish the slave trade goes down to defeat. Afterward, the film portrays Pitt as one of his few friends and allies remaining in Parliament, however even their relationship becomes strained. Pitt, now facing the stresses of leading a shaky coalition during the French Revolutionary Wars, tells Wilberforce that his cause must now wait for a more stable political climate.
Wilberforce keeps up the fight but after years of failure he is left exhausted and frustrated that he was unable to change anything in the government. Believing his life's work has been in vain, he becomes physically ill, suffering from chronic colitis which causes him to become addicted to laudanum prescribed for the crippling pain, which brings the story back up to 1797. Having virtually given up hope, Wilberforce considers leaving politics forever. Barbara convinces him to keep fighting because there is no other person who is willing or able to do so. A few days afterward, William Wilberforce and Barbara marry. Several years pass with no further success. Wilberforce's wife and new children provide him with the support and strength needed to carry on the fight.
Finally, with a renewed hope for success Wilberforce devises a backdoor method of slowly weakening the slave trade through seemingly innocuous legislation. Aided by Thornton, Clarkson, and new ally James Stephen and cheered on by the now terminally ill Pitt, he reintroduces his bill to abolish the slave trade. In time, after the 20-year campaign and many attempts to bring legislation forward, he is eventually responsible for a bill being passed through Parliament in 1807, which abolishes the slave trade in the British Empire forever.
Ioan Gruffudd as William Wilberforce
Romola Garai as Barbara Spooner
Benedict Cumberbatch as William Pitt the Younger
Albert Finney as John Newton
Michael Gambon as Charles James Fox
Rufus Sewell as Thomas Clarkson
Youssou N'Dour as Olaudah Equiano
Ciarán Hinds as Banastre Tarleton
Toby Jones as William, Duke of Clarence
Nicholas Farrell as Henry Thornton
Sylvestra Le Touzel as Marianne Thornton
Jeremy Swift as Richard the Butler
Stephen Campbell Moore as James Stephen
Bill Paterson as Henry Dundas
Nicholas Day as Sir William Dolben
Georgie Glen as Hannah More
Based on true events