Radcliffe was born in Queen Charlotte's Hospital, West London, England, the only child of Alan George Radcliffe, a literary agent, and Marcia Jeannine Gresham (née Marcia Gresham Jacobson), a casting agent who was involved in several films for the BBC, including The Inspector Lynley Mysteries and, most recently, Walk Away And I Stumble. Radcliffe's mother is Jewish and a native of Westcliff-on-Sea, Essex (her family's surname was anglicized from "Gershon"); his father is Protestant and originally from Northern Ireland.
Radcliffe first expressed a desire to act at the age of five. In December 1999, he made his acting debut in the BBC's televised two-part version of the Charles Dickens novel David Copperfield, portraying the title character as a young boy.