Making their way across the Grassmarket to the Cowgate and up to the High Street, the mob converged on the Tolbooth, where they were eventually able to overpower the guards. Porteous was dragged from his cell up the Lawnmarket to the West Bow and down to the Grassmarket, where he was lynched from a dyer's pole, using a rope taken from a local draper's shop.
After a short while, he was dragged down and stripped of his nightgown and shirt, which was then wrapped around his head before he was hauled up again. However, the mob had not tied his hands and, as he struggled free, they broke his arm and shoulder, while another attempted to set light to his naked foot. He was taken down a further time and cruelly beaten before being hung up again, and died a short while later, just before midnight on 7 September 1736. He was buried in Greyfriars Kirkyard, Edinburgh, the following day.
The events in Edinburgh heightened the sense of alarm in London, where the government was concerned about the threat to its management of Scotland. It was thought by Walpole, Queen Caroline and the Duke of Newcastle that Porteous had been unnecessarily sacrificed and there were even rumours that the conspiracy had involved the local city magistrates.
In February 1737 a parliamentary inquiry was held; the House of Lords initially proposed the disbanding of the town guard and removal of Netherbow Port, but subsequently dropped these suggestions. Eventually, the only punishments enforced were a £2,000 fine imposed on the city (used to support Porteous' widow) and the disbarment from all offices of the then Lord Provost Alexander Wilson.
It was variously thought that Porteous' murder was carried out by friends of those who had been shot and killed, revenge by the smugglers, a Jacobite plot, or even a conspiracy by Presbyterian extremists. However, the organisation of events seems to imply a degree of planning, thought to be the work of James Maxwell, an Edinburgh journeyman carpenter, together with a small group of city tradesmen and journeymen.
However, despite a reward of £200 being made available by the government for information, those responsible for the murder of Porteous were never found.
The events surrounding the Porteous Riots form part of the early chapters of the novel The Heart of Midlothian by Sir Walter Scott (1818), where they are recorded in graphic detail.