Porteous was arrested the same afternoon and charged with murder. He was tried at the High Court of Justiciary on 5 July 1736, where a majority of witnesses testified that Porteous had personally fired into the crowd on 14 April, although sixteen others said they had not seen him do so.

Feelings were running high in Edinburgh and the jury unanimously found Porteous guilty of murder. He was sentenced to death, the execution set to take place in the Grassmarket on 8 September 1736. Porteous was imprisoned in the Tolbooth.

Events in Scotland alarmed the government in London, and Sir Robert Walpole attempted to influence events by asking his representative in Edinburgh to become involved. But he had miscalculated, underestimating the depth of feeling in Scotland. A formal appeal was petitioned and the execution was deferred.