Guppy's mother was the Iranian author and singer Shusha Guppy (1935–2008). His grandfather on his mother's side was the philosopher and theologian Grand Ayatollah Seyyed Mohammed Kazem Assar, who held the chair of philosophy at Tehran University; his maternal cousin, Hooman Majd.
His father was the writer Nicholas Guppy (1925-2012). On his father's side he is a descendant of Lechmere Guppy, the naturalist who discovered the eponymous fish, as well as the inventor Sarah Guppy, Thomas Guppy, the engineer and business partner of Isambard Kingdom Brunel, the explorer Amelia Guppy, Sir Francis Dashwood and the Plantagenet family.
Guppy was educated at the Lycée Français Charles de Gaulle, Eton College, and Magdalen College, Oxford. In his second year, he became a member of the Piers Gaveston Society, as well as the Bullingdon Club. He was the best man at Earl Spencer's wedding to model Victoria Lockwood, his first wife; Lord Spencer was his best man in return. He was a close friend of Boris Johnson, who later became the Mayor of London, as well as of Count Gottfried von Bismarck.
He is married, has a daughter and two sons, and lives in Cape Town, South Africa.
In February 1993, Guppy was jailed for staging a faked jewel robbery and claiming £1.8 million from the insurers. Guppy claims his fraud was intended as retribution against Lloyd's of London, since his father had lost money in Lloyd's financial crisis of the 1990s. Guppy and his business partner, Benedict Marsh, hired a man to fake a robbery, discharge a firearm and tie them up. Both men were found guilty of conspiracy involving fraud, theft and false accounting at Snaresbrook Crown Court, and Guppy was sentenced to five years in prison.
Guppy also pleaded guilty in 1993 to three separate charges relating to illegal VAT claims on gold bullion later smuggled into India between October 1989 and July 1990.
During a telephone call in 1990 he asked Boris Johnson (then a journalist at the Telegraph) to provide the home address of News of the World journalist Stuart Collier. Collier had been making enquiries into Guppy's background, and in response Guppy wanted to send someone to physically assault Collier. The address was not provided and the attack never took place, but a tape of the conversation was leaked to the press in 1995.
He has written for The Spectator magazine, the Asia Times, the Independent on Sunday and The Independent, the Sunday Telegraph, and the New Statesman.