Art MacBaron O'Neill (Irish: Art mac Baron Ó Néill; died 1618) was an Irish landowner and soldier of the Elizabethan and early Stuart eras.
[1] John O'Hart referred to Art as illegitimate (i.e. not the son of Matthew's wife Siobhán).
[2] Hiram Morgan similarly referred to Art as Tyrone's half-brother.
Despite a series of defeats against the Irish Army that culminated in the burning of their capital at Dungannon and retreat into the woods, they were able to agree the Treaty of Mellifont which restored them to royal favour under the new King James I. O'Neill and his brothers were pardoned for their past activities and had their lands restored to them.
Six of his other sons died during Tyrone's Rebellion, and Brian O'Neill was hanged as an outlaw in 1607.