He was the son of Sir John St John (Bedfordshire MP) (born 1498) of Bletsoe (Bedfordshire) and Spelsbury (Oxfordshire) and his first wife Margaret, the daughter of Sir William Waldegrave.

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.

[3] The offices he held during his career included:[1] Lord St John of Bletso married twice.

He married firstly, before 8 February 1542, Agnes, the daughter of Sir John Fisher,[1] and by her had four sons and six daughters:[4] He married, before 28 August 1572, Elizabeth, the daughter of Geoffrey Chamber, and widow of Sir Walter Stonor (died 1551), Reginald Conyers (died 1560) and Edward Griffin (died 1569).