Matthew O'Neill, 1st Baron Dungannon (alias Matthew Kelly, alias Feardorcha Ó Néill; 1520–1558), was an Irish aristocrat. He was accepted by Conn O'Neill as his natural son. Matthew was challenged by his half-brother Shane O'Neill over the succession to the Earldom of Tyrone and was murdered by some of his supporters.

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Mathew was born about 1510, a son of Alison Kelly (née Roth) in Dundalk, the wife of a blacksmith in Dundalk.^[1] At the age of sixteen, Matthew was presented to Conn O'Neill, with whom Kelly had previously had an affair. Tyrone accepted that Matthew was his natural son.^[2]

Around 1536 Matthew married Siobhan, daughter of Cú Chonnacht Maguire, lord of Fir Manach.^[5]

Matthew and Siobhan had three sons:

1. Brian (died 1562), called Lord Dungannon, de jure 2nd Earl of Tyrone, murdered^[6]
2. Hugh (c. 1550 – 1616), who succeeded as the 3rd Earl of Tyrone
3. Cormac (died 1613)

Matthew also had an illegitimate son:

• Art MacBaron O'Neill (died 1618)

As part of the surrender and regrant policy brought in during the reign of Henry VIII, his father was in October 1542 made Earl of Tyrone with Matthew confirmed as his heir and made Baron of Dungannon.^[7] Both visited London to formally submit to the King.

This arrangement was disputed by Matthew's legitimate half-brother Shane O'Neill, who had a larger and more powerful following. Shane's violent response crushed the government's hope for a peaceful succession.^[8] Matthew was killed by Shane's men in 1558,^[9] a year before Conn O'Neill died.

In his attempts to gain recognition of the title of Earl of Tyrone from the Crown, Shane suggested that Matthew had not really been Conn's son, and his real father was a blacksmith from Dundalk named Kelly. Shane tried to show Matthew's claims were weak under both the English law of primogeniture as well as the Gaelic custom of the strongest member of the family inheriting. Shane received some recognition of his role as head of the Ó Néills, but he was never made an earl. Shane was killed by the MacDonnells of Antrim in 1567.