On the death of the previous ceanne fine, his first cousin Brian Mág Tighearnán, in 1362, Fergal became head of the lineage and resided in the castle of Cruachan Ua Cúbhrán, now in the townland of Coolnashinny, besides the modern town of Killeshandra.
The Annals of Ulster for 1364 state- Sitric, son of the herenagh, a prince of general fame and noble head of his own sept, died.
The Annals of Ulster for 1364 state- A great migratory incursion was made by the Clann-Muircertaigh into Magh-Nissi, and an attack was made by them on the people of Magh-Luirg, namely, by Tadhg, son of Ruaidhri Ua Conchobuir and by the nobles of his people, together with their great muster that is, with Fergal Mag Tigernain, chief of Tellach Dunchada and by Diarmait Mag Raghnaill, chief of Muinter-Eoluis, along with a muster of Gaidhil and gallowglasses.
An onset and attack of cavalry exclusively was given to each other at Ait-tighi-Mic-Coise and decisive defeat was inflicted on the people of Magh-Luirg and twelve persons were killed of the favourite nobles of Mac Diarmata and Aedh himself was injured there.
Fergal Mac Diarmata, king of Moylurg, and Aed caught up with them and gave battle to them, and killed some of their men.
The Annals of Loch Cé under the year 1367 state- A migratory excursion was made by the Clann-Muirchertaigh to Magh-Nise in hoc anno, and they went on an expedition into Magh-Luirg, viz., Tadhg, son of Ruaidhri O'Conchobhair and Ferghal Mac Tighernain, dux of Tellach-Dunchadha, and Diarmaid Mac Raghnaill, dux of Muinter-Eolais, accompanied by gallowglasses.
In 1367 The McKiernans and their allies, the Clan Muircheartaigh Uí Conchobhair, fought with the O’Reillys, O’Rourkes, Maguires and others but were banished into Burke territory.
O Raigillig, O Fergail, Mag Uidir and O Conchobair rose up against the Clan Murtagh and with their combined forces drove them out of Muinter Eolais.
In 1372 the poet Seán Mór Ó Dubhagáin wrote a poem about the tribes of Ireland- Triallam timcheall na Fodla.
[3] The McKiernans are mentioned as follows- MacTighearnain of cloaks, Support of the fair Gaoidhil; The purchaser of the poets, and their friend, Is over the vehement Teallach Dunchadha.
The Annals of Loch Cé for 1373 state- Barrdubh, daughter of O'Ruairc, wife of Domhnall Mac Tighernain, quievit.
The Annals of Breifne for 1383 state: Tuath Teallaigh nDonnchadha agas críoch Mhathghamhna uí Raghallaigh do loscadh le ceithirnuí Chonchabhair, ('The territory of Tullyhunco and the lands of Mahon O’Reilly were laid waste by the soldiers of O’Connor').