Sir Oliver St John (/ˈsɪndʒən/; c. 1598 – 31 December 1673) was an English barrister, judge and politician who sat in the House of Commons from 1640-53.

In 1638 he defended John Hampden, along with co-counsel Robert Holborne, on his refusal to pay Ship Money, on which occasion he made a notable speech which established him as a leading advocate.

[3] This did not prevent him from taking an active role in the impeachment of Thomas Wentworth, 1st Earl of Strafford, and in preparing the bills brought forward by the popular party in the House of Commons.

He defended the decision to proceed against Strafford by way of attainder on the simple ground that there are people who are too dangerous to be given the benefit of the law; he told the Commons: "it was never accounted cruelty or foul play for foxes and wolves to be knocked on the head."

Edward Hyde, 1st Earl of Clarendon, although he may have voted in favour of the attainder, later denounced St. John's speech as perhaps the most barbarous and inhumane ever made in the House of Commons.

[3] In 1651 he went to The Hague, where he led the mission (alongside Walter Strickland, with John Thurloe acting as his secretary) to negotiate a political union between England and the Dutch Republic.

[6] He published an account of his past conduct (The Case of Oliver St John, 1660), and this apologia enabled him to escape any retribution worse than exclusion from public office.

His daughter Johanna married Sir Walter St John of Lydiard Tregoze and was the grandmother of Viscount Bolingbroke.

Oliver St John plays a minor role in Traitor's Field by Robert Wilton, published in May 2013 by Corvus, an imprint of Atlantic Books.