| Margaret Beauchamp | |
| Lady St John Duchess of Somerset Lady Welles | |
| Spouse: | Sir Oliver St John John Beaufort, 1st Duke of Somerset Lionel de Welles, 6th Baron Welles |
| Issue: | Sir John St John Oliver St John Edith St John Mary St John Elizabeth St John Agnes St John Margaret St John Lady Margaret Beaufort John Welles, 1st Viscount Welles |
| Father: | Sir John Beauchamp |
| Mother: | Edith Stourton |
| Death Date: | before |
Margaret Beauchamp (– before 3 June 1482) was the oldest daughter of Sir John Beauchamp of Bletsoe, and his second wife, Edith Stourton. She was the maternal grandmother of Henry VII.
Margaret Beauchamp, born about 1410, was the daughter of Sir John Beauchamp of Bletsoe, Bedfordshire, and his second wife, Edith Stourton (d. 13 June 1441), daughter of Sir John Stourton of Stourton, Wiltshire.
In 1421, she became heiress to her only brother, John Beauchamp, who died young and unmarried, from whom she inherited the manors of Lydiard Tregoze in Wiltshire, Ashmore in Dorset, and Bletsoe and Keysoe in Bedfordshire, and, according to modern doctrine, the right to any barony of Beauchamp created by summons to Parliament directed to her great-great-grandfather, Roger Beauchamp, 1st Baron Beauchamp (d. 3 January 1380) of Bletsoe.
She married firstly Sir Oliver St John (d. 1437), son and heir of Sir John St John and Isabel Paveley, daughter and heiress of Sir John Paveley, by whom she had two sons and five daughters:
She married secondly, in 1439, John Beaufort, 1st Duke of Somerset, by whom she had one daughter:
She married thirdly, by licence dated 14 April 1447, as his second wife, Lionel de Welles, 6th Baron Welles, by whom she had one son:
She is buried with her second husband at Wimborne Minster in Dorset.
Margaret Beauchamp figures prominently in the 2010 Philippa Gregory novel The Red Queen, and was played by Frances Tomelty in the 2013 television adaptation The White Queen. Gregory also includes Beauchamp in her 2011 prequel novel The Lady of the Rivers.