John Frost (1750–1842) was an English radical and republican, known as the secretary of the London Corresponding Society.
Born in October 1750, Frost was educated at Winchester College, and became an attorney. In 1782 he was a prominent member of a group meeting at the Thatched House tavern in London, who advocated constitutional reforms. There his associates included William who corresponded with Frost on parliamentary representation, the Duke of Richmond, Lord Surrey, Lord Mahon, Major John Cartwright, John Horne Tooke, and John Wilkes.
At the beginning of the French Revolution Frost adopted republican principles, and in 1792 sheltered in his house a number of political prisoners. The same year he took a leading part in founding the Corresponding Society, for which he also acted as secretary. The Society began active propaganda for a reform of the parliamentary representation: one of its manifestoes, prepared by Frost and Thomas Hardy showed that 257 representatives of the people, a majority of the existing House of Commons, were returned by a number of voters that was less than 0.1% of the nation.
The Society for Constitutional Information was active at the same time, with both societies having branches in the provinces. The Constitutional Society elected Frost a deputy to the convention of France in 1793, his colleague being Joel Barlow, whose expenses he paid. In this character he was present at the trial of Louis XVI (1792–3), and was denounced in one of Edmund Burke's speeches as the ambassador to his murderers.