Katherine Mortimer was born at Ludlow Castle, Shropshire, England, in 1314, one of the twelve children and a co-heiress of Roger Mortimer, 1st Earl of March and Joan de Geneville, Baroness Geneville. Her paternal grandparents were Edmund Mortimer, 2nd Baron Mortimer and Margaret de Fiennes, and her maternal grandparents were Sir Piers de Geneville, of Trim Castle and Ludlow, and Jeanne of Lusignan. Her father was de facto ruler of England together with his mistress Isabella of France, Queen consort of King Edward II, until his eventual capture and execution by the orders of King Edward III, eldest son of Isabella and King Edward II. The latter had been deposed in November 1326, and afterwards cruelly murdered by assassins acting under the orders of Mortimer and Queen Isabella. Katherine was sixteen years old when her father was hanged, Tyburn, London on 29 November 1330.
Marriage
On 19 April 1319, when she was about five years-old, Katherine was married to Thomas de Beauchamp, 11th Earl of Warwick, eldest son of Guy de Beauchamp, 10th Earl of Warwick and Alice de Toeni. Their marriage required a Papal dispensation as they were related within the prohibited third and fourth degrees. Beauchamp had succeeded to the earldom at the age of two, therefore Katherine was styled Countess of Warwick from the time of her marriage until her death. The marriage had been arranged in July 1318 to settle a quarrel between the two families over the lordship of Elfael, which was thus given to Katherine as her marriage portion. For the term of his minority, Beauchamp's custody had been granted to Katherine's father, Roger Mortimer. Katherine later became an important personage at the court of King Edward III. As a sign of royal favour she was chosen to stand as one of the godmothers, along with Queen Philippa of Hainault, to the latter's granddaughter, Philippa, Countess of Ulster, in 1355. This honour bestowed on Katherine is described by 19th century author Agnes Strickland according to the Friar's Genealogy: "Her godmother also was of Warwick Countess, a lady likewise of great worthiness".
Issue
Katherine and Beauchamp together had fifteen children:
Guy de Beauchamp ; married Philippa de Ferrers, daughter of Henry de Ferrers, 2nd Lord Ferrers of Groby and Isabel de Verdun, by whom he had two daughters.
Katherine de Beauchamp; became a nun at Shouldham Priory.
Death and effigy
Katherine Mortimer died on 4 August 1369 at the age of about fifty-five. Two years before her death, in 1367, Katherine was a legatee in the will of her sister Agnes de Hastings, Countess of Pembroke. Katherine was buried in St. Mary's Church, Warwick, Warwickshire. She lies alongside her husband, who died three months after her of the Black Death. Their tomb with well-preserved, alabaster effigies can be seen in the centre of the quire. Katherine is depicted wearing a frilled veil with a honeycomb pattern and she is holding hands with Beauchamp. The sides of the tomb chest are decorated with figures of mourners, both male and female.
