The film also recounts the experiences of John Newton as a captain of slave ships and subsequent Christian conversion, which inspired his writing of the poem later used in the hymn.

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".

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.

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.

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.

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.