She was probably born in Hainaut in 1349 or 1350. Katherine's birth date may have been 25 November, as that is the feast day of her patron, St. Catherine of Alexandria. She was the daughter of Paon de Roet, a herald, and later knight, who was "probably christened as Gilles".
About 1367 she married Sir Hugh Swynford 1340-1372), a Lincolnshire man, by whom she had a son, Thomas (c. 1368-1433), who was a friend and companion of Henry IV both before and after he came to the English throne. Soon after her husband's death in 1372 Catherine became the mistress of John of Gaunt, and in 1396, nearly two years after the duke had become a widower for the second time, she was married to him at Lincoln. She died at Lincoln on the 10th of May 1403. By John of Gaunt Catherine had four children, all of whom were born before their marriage. They were declared legitimate in 1397 and took the name of Beaufort from one of their father's castles in Anjou.
Katherine Swynford is the subject of numerous novels, including Anya Seton's Katherine, published in 1954. Swynford is also the subject of non-fiction work, such as Alison Weir's 2008 biography Katherine Swynford: The Story of John of Gaunt and his Scandalous Duchess (ISBN 0-224-06321-9) and Jeannette Lucraft's historical biography Katherine Swynford: The History of a Medieval Mistress. Lucraft's book seeks to establish Swynford as a powerful figure in the politics of 14th-century England and an example of a woman's ability to manipulate contemporary social mores for her own interests.
Katherine's children by Hugh Swynford were:
Margaret Swynford (born c. 1369), became a nun at the prestigious Barking Abbey in 1377 with help from her future stepfather John of Gaunt, where she lived the religious life with her cousin Elizabeth Chaucer, daughter of the famous Geoffrey Chaucer and Katherine's sister Philippa de Roet.
Sir Thomas Swynford (1367–1432), born in Lincoln while his father Sir Hugh Swynford was away on a campaign with the Duke of Lancaster in Castile fighting for Peter of Castile.
Blanche Swynford, named after the Duchess of Lancaster and a godchild of John of Gaunt. (If, as suggested, she was born after 1375, this date is too late for her to have been fathered by Hugh Swynford, who died in 1371/2. However, since John of Gaunt obtained a dispensation for his marriage to Katherine for being Blanche Swynford's godfather, this theory can be discarded).
Katherine's children by John of Gaunt were:
John Beaufort, 1st Earl of Somerset (1373–1410);
Henry, Cardinal Beaufort (1375–1447);
Thomas Beaufort, Duke of Exeter (1377–1426);
Joan Beaufort, Countess of Westmorland (1379–1440).
He was a herald and knight from Hainaut who was involved in the early stages of the Hundred Years War.
He was an English nobleman and member of the House of Plantagenet, the third of five surviving sons of King Edward III of England and Philippa of Hainault.
He was an English military commander during the Hundred Years' War, and briefly Chancellor of England.
He was an English nobleman and politician.
He was a medieval English clergyman, Bishop of Winchester, a member of the royal house of Plantagenet, and a Cardinal of the Roman Catholic Church.
He was the fourth of the four children (and only daughter) of John of Gaunt, 1st Duke of Lancaster, and Katherine Swynford.
