He was born at Carnally, Creggan parish, near Crossmaglen, in County Armagh, modern-day Northern Ireland, about 1720. His father's name is unknown although his mother was Aine. A grandfather was said to have been killed at the Battle of Aughrim in 1691. McMurphy had four sisters; one of whom, Aillidh, was married to Mr. Duffy, a nephew of the poet Niall McMurphy to whom he was closely related. He was noted as a handsome man, and used to introduce himself to his victims as "Meet Seamus Mac Murphy, the handsomest man in Ireland.". He had a reputation as a great drinker and a charming companion of many women. Yet it was over-indulgence in drink and promiscuity that were to lead to his downfall.
The two were active Jacobites in the years up to the 1745 rebellion; McMurphy was an active rapparee since at least 1740. His main adversary was John Johnson of Roxborough, known as Johnson of the Fews, a tory hunter.
In the summer of 1744, as a result of the unrest caused by the Slieve Gullion meeting, Johnson was attacked and very seriously wounded. Though he survived, he met with McMurphy and Ó Doirnín, where they agreed to "an uneasy truce."
Molly MacDecker
McMurphy and Ó Doirnín often attended a sibín or inn at Flagstaff, a mountain route to Omeath, owned by Patsy MacDecker, known as Paddy of the Mountain. The area remains particularly remote even in the 21st century, and in the 1740s was the perfect hideaway for raparees. McMurphy became a lover of Mac Decker's daughter, Molly. However, the affair was tempestous; after a fierce argument and break-up, Molly swore revenge on Mac Murphy. To this end, she plied Ó Doirnín with drink one evening, and inveigled him to compose a satirical poem about Johnson, which he called The Heretic Headhunter. She took the poem to Johnson, saying McMurphy was the author. Johnson was angry at this breach of their truce. Molly was offered fifty pounds by Johnson to trap McMurphy. However, another version lays the blame on a lieutenant of Mac Murchaidh, Art Fearon, who wished to ingratiate himself with Molly. This version claims that he told her in-depth stories about infidelities McMurphy had with other women. Paddy of the Mountain decided to take advantage of the fifty pounds offered as reward money, and joined the scheme. On the Saturday night before the Pattern of Killeavy, McMurphy was to spend the night at the inn; the MacDeckers were to get him insensibly drunk and off-guard. However it came about, Johnson and his men caught McMurphy at MacDecker's inn, sometime late in 1749 or early in 1750.
Trial and aftermath
McMurphy spent eight months in prison in Newry, County Down, before been tried, found guilty and sentenced to execution. He is said to have had not fear on the day and forgave all who helped his capture, including Molly. His body was left hanging for three days before it was taken down, waked for two nights at his mother's barn in Carnally, before been buried in Creggan churchyard. In 1973, Jem Murphy, a descendant of the family, erected a memorial headstone to Seamus and the McMurphy clan. Paddy MacDecker is said to have received his blood money at Armagh in copper coin, so disgusted with the authorities with him. Folk legend has it that the effort of carrying the reward twenty miles home caused him to die within sight of his home. Molly MacDecker became ostracised by her community, and became mentally ill. She eventually drowned herself at Narrow Water.
