As a child, Johnson lived in New York, London, and Brussels before attending boarding school in England. He won a scholarship to Eton College and later studied classics at Balliol College, Oxford, where he was president of the Oxford Union. After briefly working as a management consultant, Johnson embarked on a career in journalism. He started as a reporter for The Times (Times, The) in 1987 but was fired for fabricating a quotation. He then began working for The Daily Telegraph (Daily Telegraph, The), where he served as a correspondent covering the European Community (1989–94) and later as an assistant editor (1994–99). In 1994 Johnson became a political columnist for The Spectator (Spectator, The), and in 1999 he was named the magazine's editor, continuing in that role until 2005.

In 1997 Johnson was selected as the Conservative candidate for Clwyd South in the House of Commons, but he lost decisively to the Labour Party incumbent Martyn Jones. Soon after, Johnson began appearing on a variety of television shows, beginning in 1998 with the BBC talk program Have I Got News for You. His bumbling demeanour and occasionally irreverent remarks made him a perennial favourite on British talk shows. Johnson again stood for Parliament in 2001, this time winning the contest in the Henley-on-Thames constituency. Though he continued to appear frequently on British television programs and became one of the country's most recognized politicians, Johnson's political rise was threatened on a number of occasions. He was forced to apologize to the city of Liverpool after the publication of an insensitive editorial in The Spectator, and in 2004 he was dismissed from his position as shadow arts minister after rumours surfaced of an affair between Johnson and a fellow journalist. Despite such public rebukes, Johnson was reelected to his parliamentary seat in 2005.

Johnson entered into the London mayoral election in July 2007, challenging Labour incumbent Ken Livingstone (Livingstone, Ken). During the tightly contested election, he overcame perceptions that he was a gaffe-prone and insubstantial politician by focusing on issues of crime and transportation. On May 1, 2008, Johnson won a narrow victory, seen by many as a repudiation of the national Labour government led by Gordon Brown (Brown, Gordon). Early the following month, Johnson fulfilled a campaign promise by stepping down as MP.

Johnson wrote numerous books, including Lend Me Your Ears (2003), a collection of essays; Seventy-Two Virgins (2004), a novel; and The Dream of Rome (2006), a historical survey of the Roman Empire.