Sir Nicholas Exton (died 1402) was a medieval English merchant. A leading member of the Fishmongers' Company and citizen of the City of London, he was twice elected Mayor of that city during the troubled years of the reign of King Richard II. Little is known of his personal background and youth, but he became known at some point as a vigorous defender of the rights of his Guild. This eventually landed him in some trouble for attacking the then-current Mayor, and he was fined and imprisoned as a result. The situation soon reverted to his favour with the election as Mayor of Nicholas Brembre, a close ally of his. During this period Brembre was a loyal supporter of the King, who at this time was engaged in a bitter conflict with some of his nobles (known collectively as the Lords Appellant).