Born Paul Martin in the Parsons Green area of London, he gained his earliest professional credits under that name. On joining Equity he found that the name Paul Martin was already taken, so he renamed himself after Merton, the district of London where he grew up.
His breakthrough as a television performer came as on the improvised comedy show Whose Line Is It Anyway from 1988 onwards. Have I Got News For You started in 1990, and two series of his own sketch show Paul Merton: The Series followed soon after. Since 1999 he has been the host of Room 101, a chat show in which guests are offered the chance to discuss their pet hates and consign them to the oblivion of Room 101.
Shortly before becoming a household name on HIGNFY, Merton had suffered a mental breakdown, about which he has since talked frankly.
He has been a member of the London improv group The Comedy Store Players since 1985, and still regularly performs with them.