Dolly's Brae is a road with a difficult pass in County Down. On July 12, 1848, a large assembly of Ribbonmen gathered with the intent of stopping the traditional march of Orangemen to Tollymore. The Orangemen were forewarned and avoided the Brae that year. Naturally, the opposition had a field day with that and songs appeared about their cowardice. So in 1849, the Orangemen went through the Brae without problem. On the return from Castlewellan, they were ambushed at the Brae. They were prepared for such an eventuality and their return fire dropped over a score of men, without sustaining any losses themselves.

Dolly's Brae was an exclusively Catholic village, and the Orange Order had never marched through it before. The government had been warned that in 1849 they had decided to use this route and, in anticipation of the likelihood of trouble in Dolly's Brae, they sent a company of dragoons, additional police, and magistrates to the village. They allowed the march to go ahead, however. The march through Dolly's Brae on the morning of the twelfth was peaceful, even though the Orangeman were described as being "armed to the teeth" and they sang anti-Catholic songs as they passed through the village.

The dead included Hugh King, a 10-year-old who died of gunshot wounds, and Anne Taylor, an 85-year-old woman whose death was caused by her skull being struck with a blunt instrument.
In the afternoon, the Orange lodges from the surrounding areas met at the estate of Lord Roden in Castlewellan, he urged them to "do their duty as loyal, Protestant men." About 1,500 Orangemen returned through Dolly's Brae in the evening. By this stage, about 500 Catholics had gathered in the village, armed with muskets or pikes. The conflict was triggered by the firing of a single gunshot, later reports attributed it to the Catholic side. The fighting was swift and brutal, but the military and constabulary initially did not get involved in the conflict or attempt to stop it. By the time they did intervene, ten houses and the Catholic Church had been burnt to the ground. Five Catholics also had been killed and nine others badly wounded. The dead included Hugh King, a 10-year-old boy who died of gunshot wounds, and Anne Taylor, an-85-year-old woman, whose death was caused by her skull being struck with a blunt instrument. Thirty-five Catholics were arrested, but no Orangemen.

The incident at Dolly's Brae quickly became embedded in unionist mythology as a significant victory of Protestantism over Catholicism. Lord Roden was proclaimed the hero of the day. A long-term consequence of the incident at Dolly's Brae was the passing of a Party Processions Act in 1850 that banned the July 12th marches in Ireland. This legislation had only limited success. Some marches continued to be held and in 1857, 1864, and 1867 they were accompanied by violent sectarian fighting. On each occasion, the police, the military, and the government proved reluctant to intervene to stop the parades, even though they were illegal. Instead, in 1872 the marches were again made legal as a way of appeasing Orangemen in Ireland.