He mustered many armies against the Irish, and due to his harsh methods as Justiciar, he received criticism from King Henry III of England.
He was born in Ireland in 1194, the son of Gerald FitzMaurice, 1st Lord of Offaly and Eve de Bermingham (died between June 1223/December 1226).
[5] In 1245, Maurice was dismissed from his post as Justiciar as a result of tardiness in sending the King assistance in the latter's military campaigns in Wales.
He married Juliana de Grenville and had four sons: In 1257, Maurice and his Norman army engaged the forces led by Gofraidh Ó Domhnaill (Godfrey O'Donnell), King of Tír Chonaill at the Battle of Credan, in Cairbre Drom Cliabh, now the northern part of County Sligo.
In the Annals of the Four Masters, 1257 his death is described thus: "Maurice FitzGerald for some time Lord Justice of Ireland and the destroyer of the Irish, died."
Upon his death, the properties of Lea, Rathangan, and Geashill passed to his grandson Maurice, son of Gerald Fitzmaurice, who died in 1243.