[1] Preston was a captain of the 29th Regiment of Foot, part of the British garrison in Boston under the overall command of Thomas Gage.
He was present at the Boston Massacre, also known as the Incident on King Street, when on 5 March 1770 a group of soldiers from the 29th fired on colonists of the city, after an aggressive mob had confronted them and thrown snowballs, clubs, and rocks at them.
Charges were brought against him and other soldiers, but he was acquitted in a trial held in Boston, Massachusetts.
An eyewitness report by John Tudor, who was a merchant, says that Preston gave the order to fire, but many historians believe that he did not.
Two of his men, Hugh Montgomery and Matthew Kilroy, were found guilty of manslaughter.