Sir Oliver St John, 1st Viscount Grandison (1559 – 30 December 1630) was an English soldier and politician who became Lord Deputy of Ireland.

[citation needed] In 1580, he was admitted a student of Lincoln's Inn; but about March 1584 he killed the well-known explorer George Best in a duel and was compelled to flee the country.

The motive for the duel is unclear, although St John's violent temper no doubt contributed to it: by his own later admission he was "by nature the child of wrath".

[citation needed] St John now sought his fortunes as a soldier abroad, and served in Flanders and in France.

In March he was placed on a commission for the relief of maimed soldiers and mariners, and made several speeches during the session; but parliament was dissolved in April, and soon afterwards Essex recommended St John to Robert Cecil as a cavalryman.

In November 1602 he was back in Ireland commanding twenty-five horse and 150 foot in Connacht, under Sir George Carew, and in the same year, he was recommended by Cecil for the office of vice-president of that province (but the arrangement does not seem to have been carried out).

St John was one of the members sent to lay the matter before James I: as a result Everard was summoned before the Privy Council and briefly imprisoned in the Tower of London, before being sent home with an admonition to keep the peace.

In December 1614 St John resigned the mastership of the ordnance; he was in England during October 1615, when the Earl of Somerset was committed to his custody, in connection with the murder of Sir Thomas Overbury.

His appointment was partly due to his close family connection with the Duke of Buckingham, by then the prime Royal Favourite, and his administration, like Chichester's, was marked by persecution of recusants.

Early in 1621, they urged his recall; and, though James commended him and protested against involving him in disgrace, he was finally commanded to deliver up the sword of state to Lord Chancellor Loftus on 18 April 1622.