On the death of his brother Brian ‘Breaghach’ Mág Samhradháin on 3 May 1294, Maghnus took the chieftaincy and moved to Coologe castle.
The poet would then leave and visit another lord's castle on the circuit, eventually returning to his own home laden with gifts.
The Annals of Ulster for the year 1299 state- Maghnus Mag Shamhradhain, chief of TellachEathach, died.
The Annals of the Four Masters under the year 1303 state- Manus Magauran, Chief of Teallach Eachdhach Tullyhaw, in the county of Cavan died.
The Annals of Loch Cé under the year 1303 state- Maghnus Mac Shamhradhain, dux of Tellach-Echach, occisus est.
The Annals of Connacht for 1303 state- Magnus Mag Samradain, chieftain of Tullyhaw, was killed.
Maghnus was married to Órlaith, the granddaughter of Muireadhach of the Máigh, but there is no mention of any children in the genealogies.