Sir Nicholas Throckmorton (or Throgmorton) (c. 1515/1516 – 12 February 1571) was an English diplomat and politician, who was an ambassador to France and played a key role in the relationship between Elizabeth I and Mary Queen of Scots.

Nicholas Throckmorton was the fourth of eight sons of Sir George Throckmorton of Coughton Court, near Alcester in Warwickshire and Katherine, daughter of Nicholas Vaux, 1st Baron Vaux of Harrowden, and an uncle of the conspirator Francis Throckmorton. He was brought up in the households of members of the Parr family, including that of his cousin Catherine Parr, the last wife of Henry VIII. He got acquainted with young princess Elizabeth when he was serving in the household of the former queen and her new husband Thomas Seymour and became a close confidante. In his youth he also became favourable to the Protestant reformation.

After the execution of Thomas Seymour in 1549 and the downfall of the Duke of Somerset in the same year, Throckmorton managed to distance himself from those affairs and eventually became the part of the circle of John Dudley and confidante of the young king Edward VI.

He sat in Parliament from 1545 to 1567, initially as the member for Devizes (a seat previously held by his brother, Clement Throckmorton). During the reign of Edward VI he was in high favor with the regents.

In 1547, he was present at the Battle of Pinkie Cleugh during the invasion of Scotland. He was knighted in 1551, and the title included numerous benefits, including land grants, that gave him financial security. He held the post of under-treasurer at the Tower mint from 1549 to 1552.

After the death of Edward VI in 1553, during the short-lived attempt to place Lady Jane Grey on the throne, Throckmorton tried to keep contact with both supporters of both her and Queen Mary Tudor. Eventually he began to support the latter.

However, in January 1554 he was suspected of complicity in Wyatt's Rebellion and arrested. Later historians have suspected he was at least involved either because of his Protestantism or due to his dismay on the growing Spanish influence in the court.

Throckmorton was brought to trial at the Guildhall on 17 April of that year. He managed to convince the jury of his innocence even if the court was openly hostile to him. The judges included Sir Roger Cholmeley who was trying to impress the Catholic Mary. As a result, the court fined and imprisoned the jury and sent Throckmorton to the Tower. When he was released the next year, he fled to France in exile. Though there were people who wanted to put him to trial again, he was pardoned in 1557, and was employed by Queen Mary.

After Elizabeth's accession in November 1558, Throckmorton rose rapidly into favour due to his personal acquaintance to her, sending her advice in the formation of her government. She followed some of that advice. He became Chief Butler and chamberlain of the exchequer, and from May 1559 to April 1564 he was ambassador to France. Throckmorton continued to send letters and messengers with advice to the Queen and she often followed them.

In these years Throckmorton also became acquainted with Mary Queen of Scots. He conducted the negotiations after her return to Scotland, and though he supported the Reformation, he became her close friend, willing to assist her, and do her personal favours.

As an ambassador Throckmorton encouraged Elizabeth to aid the Huguenots, and surreptitiously took a part in the war of religion. When Throckmorton returned to France from a brief trip to England in 1560, Roman Catholic leader, the Duke of Guise imprisoned him as a persona non grata. Guise was convinced that Throckmorton had been involved with the Tumult of Aboise, a Huguenot plot. Throckmorton later remarked that he was afraid he would be killed but was later released and retained his post as an ambassador.

In 1562, when religious violence began to intensify in France, Throckmorton wanted to support mediation efforts of Catherine de' Medici. Later in 1562, when the Huguenot Prince of Condé had taken over Newhaven (modern-day Le Havre) in April, Throckmorton convinced the Queen to send military aid to Huguenots in what was later called the Newhaven expedition. English troops garrisoned Le Havre in October 1562 but soon fell afoul with Huguenots. After the negotiations, the Huguenots turned against the English. After outbreak of plague, they had to surrender the next year. Catherine de' Medici was suspicious of Throckmorton's schemes, however, and when Elizabeth sent him to negotiate with her in 1563, she placed him under house arrest.

Elizabeth sent Sir Thomas Smith to negotiate his release. The two men soon begun to dislike each other and in one stage almost came to blows but Throckmorton was eventually released in 1564.

After Throckmorton's return to England, the Queen sent him as an ambassador to Scotland in May 1565. His mission was to prevent a marriage of Queen Mary and Darnley, but he failed. After the murder of Darnley, Elizabeth sent Throckmorton to Scotland in June 1567. The Scottish barons had just imprisoned Queen Mary, and Elizabeth wished the barons to restore Mary to her authority. Throckmorton himself had recommended that Elizabeth should support the Barons.

Throckmorton was working against his own advice and had contradictory orders from both his Queen and Sir William Cecil. The Scottish barons knew him as a friend of Queen Mary and as a supporter of her claim to be a successor to Elizabeth, so he was an unwelcome quest. Some of Elizabeth's messages also offended the barons. Throckmorton tried to secure the personal safety of the Queen Mary but offended Elizabeth when she showed his instructions to the Scottish barons and was recalled in August.

In 1569 Throckmorton was suspected of involvement in the Duke of Norfolk's conspiracy in favour of Mary, and was imprisoned for a time at Windsor. Throckmorton might have erroneously believed that Norfolk's idea would suit the wishes of the Queen. He was not put to trial but did not regain the Queen's confidence afterwards.

Nicholas Throckmorton died on 12 February 1571, and is buried in the church of St. Catherine Cree, Aldgate, where there is a monument to his memory.

Throckmorton married Anne Carew, daughter of Sir Nicholas Carew, a Knight of the Garter, and they had ten sons and three daughters. Their daughter Elizabeth became the wife of Sir Walter Raleigh. Anne married after his death Adrian Stokes, the second husband and former Master of Horse of Frances Brandon, Duchess of Suffolk.

Contemporary political figures regarded Throckmorton with respect. One of these was Sir Francis Walsingham who had worked with Throckmorton in France. In 1560 William Cecil said he would be prepared to resign if Throckmorton would take his place and spoke well of him after his death, in spite of their constant disagreements. Some contemporaries also suspected that he was a gray eminence behind Robert Dudley.

At the time of his death he held the posts of the keeper of Brigstock Park, Northamptonshire; Justice of the Peace in Northamptonshire; and Chief Butler of England and Wales. London's Throgmorton Street is named after him.