The Book of Magauran states he was called that because he had the three qualities of a High-King of Tara, i.e. gallantry, pride and hospitality.
The Annals of Loch Cé for 1277 state- A great depredation was committed by the Tellach-Echach on the Cenel-Duachain, in Glenn-dá-dhuile, on which occasion they slew Conchobhar Mac Dorchaidh, et alii multi.
The Annals of Connacht for 1277 state- The Tellach Echach made a great raid on the Cenel Luachain in Glenn da Duile, killing Conchobar Mag Dorchaid and many others.
At that time Fergal McGovern, chief of Tullyhaw, ordered every able-bodied man in his territory to assemble at the hill of Peadar-a-Vohers.
[6] Poems 1, 2, 3, 4 and 6 by Giolla Pádraig mac Naimhin, written c.1290–1298, in the Book of Magauran describe what Brian looked like then.
In the feast-hall were poets, musicians with harps, a hundred warriors and hounds held by gold-linked chains.
Brian was murdered by the Muircheartaigh Uí Conchobhair branch of the O'Connor royal house of Connacht in 1294 but some annals give a later date.
The Annals of Ulster for the year 1294 state- Brian Mag Shamradhain the Bregian, chief of Tellaeh-Eathach, was killed by Aed Ua Concobuir the Brefnian and by the Clann-Muircertaigh besides.
The Annals of the Four Masters under the year 1298 state- Brian Breaghach the Bregian Magauran, Chief of Teallach-Eachdhacih Tullyhaw, was slain by Hugh Breitneach O'Conor, and the Clann-Murtough.
[10] The Annals of Loch Cé under the year 1298 state- Brian Bregach Mac Shamhradhain, chieftain of Tellach-Echach, the most bountiful and puissant man that was in his own time, was slain by Aedh Breifnech O'Conchobhair and the Clann-Muirchertaigh, in his own house at Cuil-O'Guaire, on the third day of summer.
[11] The Annals of Connacht 1298 state- Brian Bregach Mag Samradain, chieftain of Tullyhaw, the most generous and valorous man of his time, was killed by Aed Brefnech O Conchobair and the Clan Murtagh in his own house at Coologe on the third day of summer.
Poem 9 in the Book of Magauran is dedicated to Mrs Gormlaidh O'Reilly-McGovern and was written at the time of Matthew O'Reilly's death by the poet Maol Pádraig Mac Naimhin (or Cnáimhín).
Brian's children with Maoilmheadha were Domhnall, Tighearnan, Matha, Donnchadh, Sitriug (d. 1351) and Tomás Mág Samhradháin the Second, who was chief of the clan until his death in 1340.