Brian O'Neill, Baron Dungannon

Brian O'Neill, 2nd Baron Dungannon – 12 April 1562) was an Irish aristocrat of the Elizabethan era. He was part of the O'Neill dynasty, a Gaelic family in Ulster. Brian had been imprisoned in Scotland by James MacDonnell in early 1556, but appears to have returned to Ulster in late 1558 or early 1559.

Shane tried to have the government recognise Matthew and his sons as illegitimate, but they continued to be supported by the Lord Deputy, The 3rd Earl of Sussex, in Dublin. Brian pursued his claims to the Earldom of Tyrone and lobbied the government to eject Shane from Tír Eoghain.

Brian was succeeded by his younger brother Hugh who became Earl of Tyrone and head of the Ó Néills. His other half-brothers were Cormac and Arthur. In Gaelic form he is often known as Brian mac Baron Ó Néill.