SOCIABLE, WELL connected and exceptionally rich, William Wilberforce seemed an archetypal late 18th-century gentleman. Armed, in his own words, with “a perfect command of money”, Wilberforce was a charming and popular undergraduate at Cambridge.

But nothing in his character, except a facility for making and keeping friends, seemed at all remarkable. No one would have guessed that his inquiring but slightly unfocused intellect would one day bring to an end the slave trade.

Elected to Parliament in 1780 as the MP for Hull – elected was a loose term in the 18th century: it cost him about £1 million in today’s money – he effortlessly slipped into London’s most fashionable clubs and societies. A courtly life at the fringes of power beckoned.

But two influences – a deep friendship with the future Prime Minister William Pitt the Younger, and a profound conversion to evangelical Christianity – set him on a different path. Perhaps the excesses of London clubland, with its gambling, gluttony and prostitution, finally revolted him.

“I must awake to my dangerous state,” Wilberforce concluded, “and make my peace with God.” Although faith would frame the rest of his career, it was Pitt’s influence, as William Hague’s excellent biography demonstrates, that persuaded Wilberforce not to neglect the public sphere.

“Why then this preparation of solitude?” Pitt asked him. “Surely the principles as well as the practice of Christianity are simple, and lead not to meditation only but to action.”

Religion may have rescued Wilberforce from a diffident life without a clear political compass. But, just as importantly, Pitt rescued Wilberforce from narrowly religious introspection that might have precluded a significant contribution to the public good.

For someone determined, in today’s language, “to make a difference”, Wilberforce possessed a diverse range of political gifts. Religion had furnished him with zeal and conviction; society lent him connections and grace of manner; while his friendship with the Prime Minister gave him access to the corridors of power. The only thing missing was a cause. Then, in 1787, Wilberforce determined to oppose the slave trade.

After the American Revolution and on the eve of the French, in the age of Enlightenment, the horrors of the trade were under increasing scrutiny. Montesquieu had summed up the Enlightenment case against slavery: “It is useful neither to master nor to the slave: not to the slave because he can do nothing from virtue; not to the master, because . . . he grows proud, curt, harsh, angry, voluptuous and cruel.”

In The Wealth of Nations, Adam Smith argued that slavery was an artificial constraint on individuals acting in their own self-interest, so economically inefficient.

The horrific realities of the trade were becoming more understood. With increasing demand for labour in West Indian sugar plantations, slaves were kidnapped or bought in western Africa, crammed into the holds of ships, where they were shackled together, unable even to turn around. Many did not survive. On the slave ship Zong, the slaves and crew were running out of drinking water beacuse of poor navigation by the captain. Calculating that he could save money on insurance, the captain ordered the slaves to be thrown overboard. Only one of the 133 slaves survived.

But awareness of these barbarities by no means brought unanimity among the political classes. Wilberforce’s original Bill to ban the slave trade was defeated by 163 votes to 88 in 1791. It was not until 1807, by which point he had dedicated much of his life and career to the cause, that he finally triumphed in the Commons.

But it is Wilberforce’s friendship with Pitt (about whom Hague wrote an earlier book) that prompts the most memorable strands of the book. Wilberforce prided himself on his political independence, and often publicly opposed Pitt, even on national security. But their mutual respect never faltered. Wilberforce knew that Pitt served the country rather than abstract ideals; with Wilberforce, as Pitt well understood, principle counted more than the national interest.

Both subject and author of this biography are excellent company. Hague clearly admires Wilberforce’s rare capacity to combine wit and sociability with moral high-mindedness. That was his life’s common thread, before and after his conversion. “I thank the Gods that I live in the age of Wilberforce,” one Cambridge friend remarked, “and that I know one man at least who is both moral and entertaining.”

But I couldn’t help wondering what Hague feels about the rich intellectual fabric of the political world to which Wilberforce belonged. This book provides great testimony to the grandeur of late 18th and early 19th-century political thought – the rights of man, self-determination, the role of empire, the relationship between the state and the individual, revolution and reaction, the Congress of Vienna.

What will be the definitive ideas of our own era? The Third Way? Regional assemblies? Election pledge mugs? What end would a modern Wilberforce pursue? Hague may be writing as a historian, but as the former leader of a major party, you sense it is politics that really draws him to Wilberforce. A pity, then, that he didn’t take the opportunity to compare the two ages.

HarperPress, £25; 582pp

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