The family were from the second rank of parvenu nobility elevated by the king as a reward for fierce loyalty to the Plantagenet dynasty.

In 1277, the eldest son, Madog II, died; his two young brothers, Llywelyn and Owain, were still children, leaving them, and their lands, at the mercy of his eldest brother Gruffydd Fychan I. Mortimer was appointed by King Edward Longshanks to be the guardian of Owain and Llywelyn, but four years later their bodies washed up in the River Dee; Mortimer was accused of their murder.

[full citation needed][5] In 1282, the ruling princes of Gwynedd attacked lands in the Perfeddwlad granted to King Edward under the Treaty of Aberconwy.

Chirk pledged allegiance to Edward II, and was with the young King when he went to negotiate his marriage with Isabella of France.

[full citation needed][9] On 22 May 1306, Mortimer was knighted at Westminster during Whitsuntide, thus his title made him of a suitable rank as an escort to the king.

[citation needed] Mortimer prepared to attack Griffith de la Pole (anglicized from the Welsh, Gruffydd).

His heir had died as a Royal Ward, leaving only a daughter, Hawise, who was married to Thomas de Charlton.

Griffith attacked John de Charlton in Welshpool Castle aiming to recover his property; whilst the king ignored pleas for a legal settlement.

Griffith sought the help of Thomas of Lancaster, recently married to the Lincoln heiress Alice de Lacy.

[13] Chirk was ordered by the king to break the siege, but de la Pole refused royal arbitration.

[full citation needed][14] Mortimer, Chirk and their friends were in the ascendant at court, confirmed by Parliament at York in November 1314.

John de Charlton was made Chamberlain, and Archbishop of York William Melton became Keeper of the Wardrobe.

On 28 January 1316, the Sheriff of Glamorgan and his men holding court outside the walls of Caerphilly Castle were attacked by a gang of Welshmen led by Llewelyn Bren.

A royal army of 2,150 marched north from Bristol to relieve Caerphilly, and Llewelyn surrendered at the head of the valleys.

She led an army with Earl of Arundel to besiege Baron Badlesmere, a crony of Lancaster's in Leeds Castle, Kent.

[23] His nephew, Roger Mortimer, managed to escape the Tower and fled to France, from where he ultimately joined Isabella in successful rebellion against Edward II in 1326.