Joan was born on 2 February 1286 at Ludlow Castle in Shropshire. She was the eldest child of Piers de Geneville, of Trim Castle and Ludlow, and Jeanne of Lusignan. She had two younger sisters, Matilda and Beatrice who both became nuns. Her paternal grandparents were Geoffrey de Geneville, 1st Lord Geneville and Maud de Lacy. Her maternal grandparents were Hugh XII of Lusignan, Seigneur de Lusignan, Couhe, et de Peyrat, Count of La Marche and of Angouleme, and Jeanne, Dame de Fougères.
When her father died in Ireland shortly before June 1292, Joan became one of the wealthiest and most eligible heiresses in the Welsh Marches, with estates that included the town and castle of Ludlow, and much land in Shropshire,as well as a generous portion of County Meath in Ireland.. She was due to inherit these upon the death of her grandfather in 1314, but in 1308, Lord Geneville conveyed most of his Irish estates to Roger Mortimer.
In 1301, Joan married Roger Mortimer, (25 April 1287- 29 November 1330). He was the son of Edmund Mortimer, 2nd Baron Wigmore and Margaret de Fiennes. He was on the Council of Ordainers, which was commissioned with the purpose to restrict the power of King Edward II and reform his household. Roger and Joan had twelve children:
1. Margaret Mortimer (1307-5 May 1337). Married Thomas de Berkeley, 3rd Baron Berkeley. Had issue
2. Katherine Mortimer (1314-died 4 August 1369). Married Thomas de Beauchamp, 11th Earl of Warwick. Had fifteen children, including Thomas de Beauchamp, 12th Earl of Warwick, and William de Beauchamp, 1st Baron Bergavenny, who married Lady Joan FitzAlan. Anne Boleyn was one of their numerous descendants.
3. Beatrice Mortimer (died 16 October 1383). Married first Edward, 2nd Earl of Norfolk, and secondly, Thomas de Braose, 1st Baron Braose. Had issue by her second husband
4. Sir Edmund Mortimer (1310- 16 December 1331). Married Elizabeth de Badlesmere, by whom he had two sons, Roger Mortimer, 2nd Earl of March, and John, who died young
5. Roger Mortimer. Married Joan Le Botiller
6. Geoffrey Mortimer. Died after 1330
7. John Mortimer. Killed in a tournament after 1328
8. Agnes Mortimer. Married Laurence Hastings, 1st Earl of Pembroke. Had issue
9. Joan Mortimer ( born 1312-died between 1337-1351). Married James Audley,2nd Baron Audley. Had issue
10. Maud Mortimer. Married John de Charlton, Lord of Powys. Had issue
11. Isabella Mortimer (1313-after 1327).
12. Blanche Mortimer (c.1321-1347). Married Peter de Grandison, 2nd Baron Grandison. Had issue
Baroness Joan de Geneville 
