Thomas Watt Hamilton was born on 10 May 1952 in Glasgow, Scotland. He was the son of Thomas Watt Sr., a bus driver, and Agnes Graham Hamilton, a hotel chambermaid. When Hamilton was approximately 18 months old, his father left the family, after which his parents divorced and his father had no further contact with him.

Hamilton was subsequently raised by his maternal grandparents, James and Catherine Hamilton, who legally adopted him and changed his name to Thomas Watt Hamilton. During his childhood, the family moved to Stirling. Hamilton was led to believe that his grandparents were his biological parents and that his mother was his sister. He reportedly learned the truth about his parentage at around the age of 22, an event described as having a lasting psychological impact.

As an adult, Hamilton became involved in youth organisations and attempted to establish and lead boys’ clubs. From the early 1970s onward, concerns were repeatedly raised about his conduct with young boys. In 1973, he became involved with the Scout Association, first as an assistant leader and later as a troop leader. Within a year, multiple complaints were made regarding his behaviour, including allegations of inappropriate supervision during overnight activities. On 13 May 1974, his Scout warrant was withdrawn, with senior officials stating concerns about his moral intentions. He was subsequently barred from holding future leadership positions within the organisation.

Over the following decades, Hamilton continued to complain to authorities, politicians, and public figures, alleging that rumours and police actions had unfairly destroyed his reputation and livelihood. He corresponded with individuals including Queen Elizabeth II and his local Member of Parliament. Despite prior police investigations and reports describing him as unsuitable to own firearms, Hamilton legally retained access to guns.

On the morning of 13 March 1996, Thomas Hamilton carried out a mass shooting at Dunblane Primary School in Dunblane, Scotland. At approximately 8:15 a.m., he was seen outside his home in Stirling before driving to Dunblane, arriving at the school grounds at around 9:30 a.m. After parking his van, Hamilton cut nearby telephone cables before entering the school premises.

Armed with four legally owned handguns two 9mm Browning pistols and two Smith & Wesson .357 Magnum revolvers—and carrying 743 rounds of ammunition, Hamilton entered the school gymnasium where a Primary 1 class of young pupils was preparing for a physical education lesson.

Hamilton opened fire rapidly and indiscriminately. Within a span of approximately three to four minutes, he shot teachers and children at close range. Sixteen pupils aged five and six and one teacher, Gwen Mayor, were killed. Fifteen other people were injured, many seriously. One child later died while being transported to hospital.

After firing 106 shots, Hamilton returned to the gymnasium, placed a revolver in his mouth, and killed himself.

Emergency services were alerted shortly after the shooting began. Medical teams arrived within minutes and transported the wounded to nearby hospitals. By late morning, all surviving victims were receiving treatment.

The massacre remains the deadliest mass shooting in British history. In the aftermath, a public inquiry led to the Cullen Report, which recommended sweeping changes to firearms legislation. These recommendations resulted in the near‑total ban on private handgun ownership in Great Britain, marking a significant shift in UK gun control law.