Alexander Crichton of Brunstane, (died before December 1558), was a Scottish Protestant laird who advocated the murder of Cardinal David Beaton and supported the plan for the marriage of Mary, Queen of Scots and Prince Edward of England. In contemporary letters and documents Alexander is known by variant spellings of "Brunstane," his territorial designation. The original House of Brunstane was near Penicuik, and another Crichton estate at Gilberstoun near Portobello, Edinburgh later became known as Brunstane.

Alexander Crichton went to France carrying royal letters in 1539 and as a servant of Cardinal Beaton. On his return in February 1540 his ship was forced by a storm to anchor in an English harbour. Subsequently, the English ambassador in Scotland Ralph Sadler tried to embarrass and discredit Cardinal Beaton in front of James V of Scotland with compromising letters captured from Brunstane's bag. James V however argued in favour of the Cardinal that he had a separate spiritual authority in Scotland apart from the King's own temporal powers. Later, when the Cardinal was present, James and Ralph compared the captured letters with Beaton's copies, and found a discrepancy. James V thanked Sadler and his uncle Henry VIII but would not find fault in the Cardinal's actions.

Alexander Crichton remained in the Cardinal's favour and sailed with him to France in 1540. He returned before his master in 1541 to meet James V. The King, Crichton, and the secretary, Thomas Erskine of Haltoun, played tennis at St Andrews on 3 April 1541. In November 1542 he sailed to France from Dumbarton on the business of rents owed to the Cardinal and Mary of Guise. He returned with money for James V from Francis I of France and was later accused of keeping some of it. An English spy said of Alexander's return in December 1542 that he had brought "little comfort." On 19 November 1542 he and his son John were rewarded for Alexander's services and expenses in France with a new charter for part of their Gilberstoun estate.

After the death of James V in December 1542, Scotland was ruled by a Governor, Regent Arran. By now Alexander Crichton of Brunstane was receiving an English pension as a supporter of English political and Protestant religious policy in Scotland. In July 1543 Cardinal Beaton and his allies who opposed Regent Arran and pro-English initiatives camped with up to 6,000 armed men at Linlithgow, where Mary, Queen of Scots was kept in the Linlithgow Palace. Alexander Crichton told Ralph Sadler that the principal cause of this rebellion was to break the peace with England, the recently signed Treaty of Greenwich. This peace agreement provided that Mary, Queen of Scots would marry the English Prince Edward when she was of age. In his report to England, Sadler contrasted Crichton's and George Douglas's account of the situation with the statement of the Earl of Glencairn, that the rebel party were happy with the marriage plan and only concerned with the detail of when Mary would be sent to England.

The Governor and the Cardinal were reconciled. Crichton continued to correspond with Ralph Sadler. In November 1543, when Sadler had been forced to move from Edinburgh to Tantallon Castle and the English marriage plan was losing support in Scotland, Brunstane wrote that he was continuing to recruit supporters for English policy, and mentions John Charteris and John Sandilands of Calder. He persuaded Sandilands's neighbours to refuse offers of French payments.

At the opening of the war of the Rough Wooing in March 1544, Brunstane met the English Berwick Pursuivant, Henry Ray secretly in Edinburgh and gave him letters he had written for Henry VIII. In April 1544, he proposed the murder of Cardinal Beaton, while Lord Hertford was planning the invasion that resulted in the burning of Edinburgh in May. The offer was not taken up, but Brunstane was given a cipher code to use in his English letters. Brunstane employed a Scot called Wishart to take his plan for the Cardinal to Lord Hertford on 17 April 1544, who noted for Henry VIII its two objectives;

One is, that the Larde of Grange, late Tresourer of Scotlande, the Master of Rothes, th'earl of Rothers eldest son, and John Charters, wolde attempte eyther to apprehende or slee the Cardynall at some tyme when he shall passe thorough the Fyf lande, ...,
The other is, that in case Your Majestie would grant unto them a convenyent enterteynnment for to kepe 1,000 or 1,500 men in wages for a moneth or two, ..., they will take uppon them, at such tyme as Your Majesties armye shalbe in Scotland, to destroye the abbey and town of Arbroath ..., and t'apprehende all those whiche they say be the principall impugnators of amyte bitwen Englande and Scotlande"

One is, that the laird of Grange, lately Treasurer of Scotland, the Master of Rothes, the earl of Rothes's eldest son, and John Charteris, would attempt either to apprehend or slay the Cardinal at some time when he shall through Fife land.
The other is, that in case Your Majesty would grant them a convenient entertainment (finance) for 1,000 or 1,500 men in wages, they will undertake at such time as Your Majesties army shall be in Scotland, to destroy the Abbey and town of Arbroath, and apprehend all those which they say be the principal opponents of the amity between England and Scotland

The historian Charles Rogers discussed the identity of Brunstane's messenger "Wishart." Rogers argued that the priest and master of arts and Protestant preacher George Wishart would not simply be called "Wishart" in this correspondence, and suggested the messenger was a young man, John, eldest son of John Wishart of Carnbeg.