He belonged to a younger branch of the Wisharts of Pitarrow. He seems to havegraduated M.A., probably at King's College, Aberdeen, and taught as a schoolmaster at Montrose. Accused of heresy in 1538, he fled to England, where a similar charge was brought against him at Bristol in the following year. In 1539 or 1540 he started for Germany and Switzerland, and returning to England became a member of Corpus Christi College, Cambridge.
In 1543 he went to Scotland in the train of a Scottish embassy which had come to London to consider the treaty of marriage between Prince Edward (later Edward VI of England and the infant Mary I of Scotland. He may have been the Wishart who in April 1544 approached the English government with a proposal for getting rid of Cardinal David Beaton. Roman Catholic historians such as Alphons Bellesheim, and Anglicans like Canon Dixon, have accepted the identification. However, there was another George Wishart, bailie of Dundee, who allied himself with Beaton's murderers; and Sir John Wishart (d. 1576), afterwards a Scottish judge, may also claim the doubtful distinction.
His career as a preacher began in 1544, and the story has been told by his disciple John Knox. He went from place to place, in danger of his life, denouncing the errors of Rome and the abuses in the church at Montrose, Dundee, Ayr, in Kyle, at Perth, Edinburgh, Leith, Haddington and elsewhere. At Ormiston, in December 1545, he was seized by the Earl of Bothwell, and transferred by order of the privy council to Edinburgh castle on January 19, 1546. Thence he was handed over to Cardinal Beaton, who had him burnt at St Andrews. John Foxe and Knox attribute to him a prophecy of the death of the Cardinal, who was assassinated on May 29 following, partly in revenge for Wishart's death.
Foxe's Acts and Monuments; Hay Fleming's Martyrs and Confessors of St Andrews; Cramond's Truth about Wishart (1898); and Dict. of Nat. Biogr vol. lxii. (248-251, 253-254).