Ó Laoghaire marries Eibhlín Dubh Ní Chonaill, aunt of Daniel O’Connell, in 1767. She has been a widow from the age of 15 and is now 23. They have three children, Cornelius, Fiach and a third who apparently does not survive infancy.
Having returned home to Rathleigh House near Macroom, Cork, the hot-tempered Ó Laoghaire becomes involved in a feud with a protestant landowner and magistrate, Abraham Morris of Hanover Hall, Macroom. When Morris is High Sheriff of County Cork in 1771, he lays charges against Ó Laoghaire following his alleged attack on Morris and the wounding of his servant on July 13, 1771 at Hanover Hall. In October of that year, Ó Laoghaire is indicted in his absence, and Morris offers a 20 guinea reward for his capture.
The feud between the two men continues and in 1773, Morris demands that Ó Laoghaire sell him the fine horse that Ó Laoghaire had brought back from his service in the Austro-Hungarian army for £5. The Penal Laws state that no Catholic might own a horse worth more than £5 and could be forced to sell a more valuable one on demand to any Protestant at this price. Ó Laoghaire refuses to sell and challenges Morris to a duel, which Morris declines. Morris uses, or misuses, his position as magistrate to persuade his fellow magistrates to proclaim Ó Laoghaire an outlaw, who can then legally be shot on sight. Morris leads a contingent of soldiers that track Ó Laoghaire down to Carrignanimma on May 4, 1773. He gives the order to fire on Ó Laoghaire. The first shot, which kills him, is fired by a soldier called Green.
Morris and the soldiers are held to be guilty of Ó Laoghaire’s murder by a coroner’s inquest on May 17, but Morris is acquitted of the murder by Cork magistrates on September 6, 1773. Morris is shot in Cork on July 7 by Ó Laoghaire’s brother Cornelius, who sees Morris at a window of a house in Hammond’s Lane where he is lodging. He fires three shots, wounding Morris. The shots are not immediately fatal, but Morris dies in September 1775, presumably as the result of the shooting. The soldier Green is decorated for his “gallantry.”
Ó Laoghaire’s wife Eibhlín Dubh Ní Chonaill composes the long poem “Caoineadh Airt Uí Laoghaire” (Lament for Art O’Leary), mourning his death and calling for revenge.
Ó Laoghaire’s tomb at Kilcrea Friary has the epitaph likely composed by his widow:
Lo Arthur Leary, generous, handsome, brave,
Slain in his bloom lies in this humble grave.