Gruffudd plays Wilberforce, who, as a Member of Parliament, navigated the world of 18th Century backroom politics to end the slave trade in the British Empire. Albert Finney plays John Newton, a confidante of Wilberforce who inspires him to pursue a life of service to humanity. Benedict Cumberbatch is William Pitt the Younger, England's youngest ever Prime Minister at the age of 24, who encourages his friend Wilberforce to take up the fight to outlaw slavery and supports him in his struggles in Parliament.

Elected to the House of Commons at the age of 21, and on his way to a successful political career, Wilberforce, over the course of two decades, took on the English establishment and persuaded those in power to end the inhumane trade of slavery.

Romola Garai plays Barbara Spooner, a beautiful and headstrong young woman who shares Wilberforce's passion for reform, and who becomes his wife after a whirlwind courtship. Youssou N'Dour is Olaudah Equiano. Born in Africa and sent as a slave to the Colonies, Equiano bought his freedom and made his home in London, where he wrote a best-selling account of his life and became a leading figure in the fight to end the slavery of his fellow countrymen.