In the three years leading up to the Peterloo Massacre, members of the working-class repeatedly tried and failed to convince their government to improve their standard of living. The most prominent demand was to repeal the Corn Laws. Marches and gatherings were often "dispersed without injury" and petitions were rejected entirely. From the beginning of 1819, mass meetings were becoming more frequent. In response, "the government worked to find a legal justification for the magistrates to send in troops to disperse a meeting when riot was expected but not actually begun." In the end, approval was given privately, rather than officially, to turn to military action if needed and then receive forgiveness after the fact.

After being delayed for two weeks, a crowd of about 60,000 people from the surrounding region met in St. Peter's Square. Shortly after 1pm, the order was given by the local magistrate to arrest Henry Hunt, the main speaker at the meeting. The first death of the massacre was that of a two year old child who was knocked out of his mother's arms by a rushing horseman on his way to deliver the warrant. About 40 minutes later, the first of the cavalry made their way into the crowd to arrest the speakers, got stuck, and subsequently bagan hacking at the crowd with sabers. Eventually, this turned into indescriminate "dispersal" of the crowd through force of violence. Modern estimates hold that between 11 and 18 people were killed and over 600 wounded.