Oliver St John, 3rd Baron St John of Bletso (c. 1540–1618) was an English politician who sat in the House of Commons from 1588 until 1596 when he inherited the peerage as Baron St John of Bletso.
In 1588 he was elected Member of Parliament for Bedfordshire.
[2] He succeeded to the barony on the death of his brother John without male issue on 23 October 1596.
[1] He was Lord Lieutenant of Huntingdonshire from April 1597 until his death.
St John married Dorothy Reid, daughter of Sir John Rede or Reid, of Oddington, Gloucestershire.