Guy de Beauchamp was the first son and heir of William de Beauchamp, 9th Earl of Warwick, (c. 1238 – 1298).
His mother was Maud FitzJohn, daughter of John fitz Geoffrey, who was Justiciar of Ireland and a member of the council of fifteen that imposed the Provisions of Oxford on King Henry III.
William was the nephew of William Maudit, 8th Earl of Warwick, and when his uncle died without issue in 1268, he became the first Beauchamp earl of Warwick.
In 1271 or 1272 his first son was born, and in reference to the new family title, William named his son after the legendary hero Guy of Warwick.
William de Beauchamp was a capable military commander, who played an important part in the Welsh and Scottish wars of King Edward I.
A marriage between Guy and Isabel de Clare, daughter of Gilbert de Clare, 6th Earl of Hertford, was contemplated, or possibly even took place and then annulled.
It was not until early 1309 that Guy married Alice de Toeni, a wealthy Hertfordshire heiress.
By this time Guy had already succeeded as Earl of Warwick, after his father's death in 1298.

By his wife, Alice, Guy had two sons, Thomas, his heir and successor, and John de Beauchamp, Lord Beauchamp KG (1315 – 2 December 1360); he carried the royal standard at the Battle of Crecy, and two daughters,
Maud de Beauchamp (died 1366), married before Easter term 1332 Geoffrey de Say, 2nd Lord Say, by whom she had issue.
The Barons Saye and Sele are their descendants.

Elizabeth de Beauchamp (c. 1316 – 1359), married before Easter term 1332 Thomas Astley, 3rd Lord Astley, by whom she had two sons, William Astley, 4th Lord Astley and Sir Thomas Astley, ancestor of the Astleys of Patshull and of Everley.

By an unknown mistress (or mistresses), Earl Guy also had three daughters:
Isabel de Beauchamp; married John de Clinton.

Emma de Beauchamp; married Roland de Oddingseles.

Lucia de Beauchamp (also known as Lucy); married Robert de Napton, Knt.
The son of Sir Adam Napton Lucia and Sir Robert had a son Adam Napton; he married Margaret Helier
Guy de Beauchamp was the first son and heir of William de Beauchamp, 9th Earl of Warwick, (c. 1238 – 1298). His mother was Maud FitzJohn, daughter of John fitz Geoffrey, who was Justiciar of Ireland and a member of the council of fifteen that imposed the Provisions of Oxford on King Henry III. William was the nephew of William Maudit, 8th Earl of Warwick, and when his uncle died without issue in 1268, he became the first Beauchamp earl of Warwick. In 1271 or 1272 his first son was born, and in reference to the new family title, William named his son after the legendary hero Guy of Warwick. William de Beauchamp was a capable military commander, who played an important part in the Welsh and Scottish wars of King Edward I.
A marriage between Guy and Isabel de Clare, daughter of Gilbert de Clare, 6th Earl of Hertford, was contemplated, or possibly even took place and then annulled. It was not until early 1309 that Guy married Alice de Toeni, a wealthy Hertfordshire heiress. By this time Guy had already succeeded as Earl of Warwick, after his father's death in 1298.
By his wife, Alice, Guy had two sons, Thomas, his heir and successor, and John de Beauchamp, Lord Beauchamp KG (1315 – 2 December 1360); he carried the royal standard at the Battle of Crecy, and two daughters,
Maud de Beauchamp (died 1366), married before Easter term 1332 Geoffrey de Say, 2nd Lord Say, by whom she had issue. The Barons Saye and Sele are their descendants.
Elizabeth de Beauchamp (c. 1316 – 1359), married before Easter term 1332 Thomas Astley, 3rd Lord Astley, by whom she had two sons, William Astley, 4th Lord Astley and Sir Thomas Astley, ancestor of the Astleys of Patshull and of Everley.
By an unknown mistress (or mistresses), Earl Guy also had three daughters:
Isabel de Beauchamp; married John de Clinton.
Emma de Beauchamp; married Roland de Oddingseles.
Lucia de Beauchamp (also known as Lucy); married Robert de Napton, Knt. The son of Sir Adam Napton Lucia and Sir Robert had a son Adam Napton; he married Margaret Helier
Guy de Beauchamp, 10th Earl of Warwick