HE’S the unsung Scots hero who played a pivotal role in consigning slavery to the history books.

But outside the dusty tomes of academia, the extraordinary story of Zachary Macaulay has largely been forgotten.

Now the final resting place of the pioneering activist – whose horrific experiences in the Jamaican plantations and forensic attention to detail helped change the world forever – is to be marked for the first time with a memorial plaque.

Born in Inveraray in 1768, Macaulay overcame a misspent youth binge-drinking on the streets of Glasgow to become the governor of Sierra Leone, and later helped lay the foundations for the abolition of slavery in 1833.

His biographer Rev Dr Iain Whyte insists Macaulay provided the crucial “ammunition” that allowed key figures such as William Wilberforce to force a change in the law.

He said: “He collected the material and Wilberforce used it. I would have to say strongly that it would have taken longer to abolish slavery but for the campaigning of people like Zachary.”

Professor John Cairns of Edinburgh University argues Macaulay's direct experience gave him “an extra moral authority”.

Despite this, his vital role is often overlooked.

A son of the manse, Macaulay left school at 14 and travelled to Glasgow to work in a merchant’s office – where he quickly fell in with a rowdy crowd and developed a taste for booze.

Things took a turn for the worse when a mysterious, shameful event led him to pack his bags and head for Jamaica. Macaulay never divulged what happened, but some have speculated the teenager got a girl pregnant.

In Jamaica, he worked as a “bookkeeper” – or slave overseer – at a sugar plantation. Just 16 years old, he was at first horrified by the brutality around him, but he hardened over time.

It was only after he returned to Britain in 1789 that he came into contact with anti-slavery campaigners and developed a fervent belief that the law must be changed. His guilt over his time in Jamaica would come to haunt him.

Through working with the evangelical Clapham Sect – a group of abolitionists with the politician William Wilberforce at their centre – Macaulay was invited to visit Sierra Leone, the African colony established to provide a home for emancipated slaves. He became its governor while still in his mid-20s.

In 1799, he returned to England on a slave ship to experience the conditions first-hand, and dedicated himself to abolition.

The slave trade was outlawed across the British Empire in 1807. But Macaulay's work wasn't finished, and he went on to launch the monthly Anti-Slavery Reporter.

His attention to detail and statistical know-how armed Wilberforce and the abolitionists with the facts they needed to argue the case for further reform in Westminster.

Slavery itself was abolished in 1833, and Macaulay died five years later. He was buried in a cemetery in London, but after the site became a public park – St George’s Gardens – the exact location of his grave was lost.

Now, to mark the 250th anniversary of his birth, a memorial plaque will be unveiled in the gardens after being donated by the Royal Statistical Society (RSS), the Friends of St George’s Gardens, University College London and the Clan Macaulay Association.

Sir David Spiegelhalter, president of the RSS, described him as an “unsung hero”. He added: “The people who quietly gather the evidence don't always get noticed, which is why we think it's so great that Macaulay's contribution is being remembered today."