Ó Muirgheasa was born in Cashlan East, Lisdoonan, Donaghmoyne, County Monaghan on 14 January 1874.
He attended Lisdoonan school but learned to read and write Irish from his granduncle, Proinsias Ó Conghaile.
[1] Ó Muirgheasa married harpist and fellow teacher, Eibhlín Ní Raghallaigh (Helen O'Reilley) of Dundalk in 1906.
Ó Muirgheasa graduated as a teacher from St. Patrick's College, Drumcondra, in 1900, obtaining a teaching post at St. Malachy's, Dundalk, in 1901, where he was one of the founders of the Louth Historical and Archaeological Society in 1903.
Ó Muirgheasa moved to Strabane, County Tyrone in 1907, where he organised the teaching of Irish in schools.