St John was a younger son of
Oliver St John, 3rd Baron St John of Bletso and his wife Dorothy Reid, daughter of Sir John Rede or Reid, of
Odington,
Gloucestershire. He was knighted on 24 July 1619 at Bletsoe together with his brother
Beauchamp, MP. Apart from Beauchamp, four other brothers,
Oliver,
Rowland,
Anthony and
Alexander were to become MPs. In 1621 St John was elected
Member of Parliament for
Huntingdon. He was re-elected MP for Huntingdon in 1624 and again in 1625. St John died without issue. His eldest brother
Oliver inherited the
Barony and became
Earl of Bolingbroke. ==References==