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.
[3] Around 1536 Matthew married Siobhan, daughter of Cú Chonnacht Maguire, lord of Fir Manach.
[citation needed] This arrangement was disputed by Matthew's legitimate half-brother Shane O'Neill, who had a larger and more powerful following.
[11] 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.