The son of Oliver St John, 1st Baron St John of Bletso, and Agnes Fisher, he succeeded to the barony upon his father's death in 1582.
In January 1585 he was appointed the keeper of Mary, Queen of Scots, at Tutbury Castle.
[3] St John married, about 1575, Katherine Dormer, daughter of Dorothy (born Catesby) and Sir William Dormer of Wing, Buckinghamshire and died on 23 October 1596 without male heirs.
His widow died in 1615 and was buried in Westminster Abbey.
This biography of a baron or baroness in the Peerage of England is a stub.