At 4am, on February 24, 1807, the House of Commons voted by 283 to 16 for the second reading of a bill to abolish the British slave trade. In an almost unprecedented gesture, nearly the entire house rose to cheer one of its members who, for two decades, had been ignored, abused or violently opposed for making the promotion of this measure his life’s work.

William Wilberforce, the Yorkshire MP, was “completely overpowered by my feelings” and sat with tears streaming down his face. His campaign had been extraordinary. He made himself perhaps the most influential back-bencher in British parliamentary history. A remarkable man espoused a great cause to the point of obsession, and thereby achieved greatness for himself.

The success of William Hague’s biography of Pitt the Younger prompted him to take on Pitt’s intimate friend Wilberforce, who flourished in an age when, as the shadow foreign secretary observes, “the readiness of MPs to switch their votes according to the arguments presented, particularly on an issue . . . where party loyalties did not apply, placed a premium on oratorical ability and persuasiveness which the rise of disciplined political parties would render almost worthless”.

Although this is a book about a politician, its appeal reaches well beyond politics. Wilberforce was born in Hull in 1759, into a family that had grown rich in the Baltic trade. As a young man, the early deaths of his father and uncle made him their sole heir, with the huge income of £8,000 a year. At Cambridge and as a 21-year-old MP (winning the Hull seat cost him £9,000) he gambled and partied with his contemporaries in an age notable for its dissipation. His relationship with Pitt was unimpaired by an incident in which the appallingly shortsighted Wilberforce almost shot him in mistake for a partridge.

He stood only 5ft 5ins high, but his voice enchanted every listener, both in song and speech. After hearing Wilberforce address a meeting, Boswell wrote: “I saw what seemed a mere shrimp mount upon the table; but as I listened, he grew and grew until the shrimp became a whale.” Wilberforce took heed of a warning from Camden, the lord chancellor, against exploitation of his gifts as a mimic, saying “it is but a vulgar accomplishment”. This was a pity, for the young MP’s imitations of Lord North were famous.

From an early age, he displayed interest in religion and appalled his mother by a dalliance with Methodism. In 1784, while on the Grand Tour with Isaac Milner, the brilliant Cambridge don, Wilberforce embraced evangelical Christianity. He renounced his fleshly sins (not that these were ever heinous) and considered also quitting politics. He was persuaded to persevere by the former slave trader John Newton, now a London parson. Newton urged him to fulfil his spiritual quest through action rather than reflection.

Wilberforce’s first initiative was ill-advised. He harnessed his new-found zeal to a crusade against vice. It was true that British society was addicted to gaming, whoring and drink on a horrific scale. The Treasury secretary wrote shamelessly to Wilberforce: “I have actually been drunk ever since 10 o’clock this morning, and have not yet quite the use of my reason, but I am, yours most faithfully and cordially, George Rose.”

But the young MP’s campaign provoked the anger of some important people and the mockery of many more. He seemed happy to ignore the excesses of the ruling class, in his eagerness to check wickedness among the poor. Sydney Smith suggested that his aim was “suppressing the vices of persons whose income does not exceed £500 a year”.

In 1787, Wilberforce changed direction. On a visit to a fellow MP, Charles Middleton, he was urged to address his energies to the slave trade. Pitt encouraged him. Wilberforce began to study the issue, and was appalled by all he learnt. He embarked on the campaign that dominated the rest of his life.

In the early years, violent opponents of Wilberforce and Thomas Clarkson, his foremost ally outside parliament, argued that slavery was economically indispensable to Britain’s mercantile life and its colonies abroad; that it was untrue that the institution was cruel. In those days, as Hague remarks, facts about almost everything were in short supply. Clarkson and others amassed an arsenal of information about the brutalities of the passage, death rates and conditions endured by captives sold in the Caribbean and the Americas.

Yet after the first big debate in the Commons promoted by Wilberforce in 1789, he did not seek a vote, because he perceived how badly he would lose. Despite the cause having the backing of both Pitt and Fox, backbench opinion was overwhelmingly hostile to abolition. The Reign of Terror across the Channel, together with the years of upheaval and war that followed, were gravely damaging to radical causes, including those of Wilberforce.

The royal family was especially hard on Wilberforce and abolition. George III’s brother Clarence told the House of Lords that slaves existed “comparatively in a state of humble happiness”. Wilberforce further damaged his case by displaying little enthusiasm for the conflict with France. War offended his deepest instincts. Paradoxically, his conservatism on British domestic issues caused him to provide warm support to Pitt on security issues. But Wilberforce’s reputation was clouded by his apparent wetness about the national mission of drubbing the French.

Through all the years of travail that followed, at no moment is Wilberforce’s story dull. There were bitterly fought elections against landowning grandees; struggles with chronic ill-health that made him dependent on opium; wide-ranging philanthropy, much of this promoted through the so-called Clapham group of like-minded rich liberals. It would be too cynical to describe his gifts for friendship as networking, but they contributed much to the ultimate success of his crusade.

At 37, he met Barbara Ann Spooner, the 20-year-old daughter of a Birmingham businessman, and married her six weeks later. Their six children became one of the passions of Wilberforce’s life, though in his old age his eldest son brought about the family’s financial ruin, by a rash investment in a dairy farm. Even after Wilberforce’s triumph in securing abolition of the trade in slaves, he battled on until his death in 1833 against the institution of slavery, which Britain ended only in 1834. He died broke but beloved, applauded for his rhetorical genius, warmth of heart and nobility of spirit. He was recognised as a national treasure, and buried in Westminster Abbey.

Books by front-line politicians are sometimes overpraised for the same reason Johnson claimed that women preachers commanded admiration, because people are amazed to see them putting pen to paper. A sceptic might say of Hague’s Wilberforce, as was suggested of his Pitt, that it is not notably original. But the author has produced a splendid read, for which he deserves the utmost credit. He tells Wilberforce’s story with such enthusiasm and narrative skill that, in this bicentennial year, his book seems assured of bestsellerdom. I put it down liking Hague as much as I was moved by his tale, one of the most remarkable in British political history.

William Wilberforce: The Life of the Great Anti-Slave Campaigner by William Hague

HarperCollins £25 pp592

Available at the Books First price of £23 (inc p&p) on 0870 165 8585

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