Whitehall was born on 7 July 1988 at the Portland Hospital in the West End of London. He is the first child of actress Hilary Amanda Jane Whitehall (née Isbister, stage name Hilary Gish) and the television producer Michael John Whitehall. His father was an agent for Judi Dench, Colin Firth, and Richard Griffiths, and wrote the 2007 memoir Shark-Infested Waters which was illustrated by Jack. Whitehall has a sister, Molly Louisa Anushka (born 23 October 1989), and one brother, Barnaby William Frances (born 10 March 1992). He had two godfathers — Nigel Havers and the late Richard Griffiths, both actors. He is a descendant of Thomas Jones Phillips, a solicitor and clerk from Newport, South Wales in the mid-19th century.
Whitehall attended Tower House School in East Sheen, west London, where he was a fellow pupil of actor Robert Pattinson. He has made jokes about this, often mentioning that he resented Pattinson's taking all the best acting roles in the school plays. He auditioned for the role of Harry Potter, but the casting director was unimpressed with Whitehall, who had not read the book.
Whitehall's parents sent him to boarding school at age 8. He attended the Dragon School in Oxford and then Marlborough College, a public school in Wiltshire. Whitehall took a gap year where he decided to pursue a career in stand-up comedy. He attended the University of Manchester for two terms only, to study History of Art.
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