Ó Mealláin was of a Tír Eoghain ecclesiastical family who were the hereditary keepers of the Bell of Saint Patrick (Clog na hUachta).
Tarlach joined a community of Franciscans who had been expelled from their convent in Armagh in the 16th century and settled in Tyrone under the protection of the Ó Neills of Cashlan.
"The Cín Lae was written in abbreviated form, apparently as a memory aid to the author who may have intended to produce a fuller history of the period at a later date.
The narrative comes to an abrupt end on the 28th line of page forty-four: "Tanic trí mile saigdeor ón Pharlemeint i nÁth C. i n-aghaidh Laighneach agus each ..." Page one: "On the eve of the Feast of Saint John Capistranus the lords of Ulster planned to seize in one night, unknown to the English and the Scots, all their walled towns, castles and bawns.
(Saturday 23 October 1641, Old Style) A reference to the Battle of Scarrifholis (June 1650) within the Cín Lae indicates that he was still alive at that date, though his diary ends in 1647.