 His paternal great-great-great-grandfather Sir Oliver St John of Bletsoe, Spelsbury and Lydiard Tregoze (d. 1437) was the husband of Margaret Beauchamp of Bletso, great-great-granddaughter of Roger de Beauchamp, who was summoned to Parliament as Baron Beauchamp of Bletso from 1363 to 1379.Since then that title had not been assumed, although St John was considered to be the line of heir.On 13 January 1559 he was raised to the peerage himself as Baron St John of Bletso, in the county of Bedfordshire.