Pearson was educated at King's College School, Wimbledon, and Peterhouse, Cambridge, where he won a double first in history. He then worked for The Economist, BBC Television and The Sunday Times. He was Ian Fleming's assistant at the Sunday Times and went on to write the first biography of Fleming, The Life of Ian Fleming', published in 1966.
Pearson has also written "true crime" biographies, such as The Profession of Violence (The most read book in Great Britain's Prisons), an account of the rise and fall of the Kray twins, who had hired him to write their biography in 1967. Over the next several years the brothers, who by now were in jail, wrote frequently to Pearson. He wrote two further books about the Krays: The Cult of Violence: The Untold Story of the Krays and Notorious: The Immortal Legend of the Kray Twins. In 2010 Pearson put up for auction more than 160 previously unseen letters and photographs from the Kray twins. The items sold for £20,780.
Pearson's book Facades was the first full-scale biography of the Sitwell siblings Edith, Osbert and Sacheverell. It was published in 1978.
Pearson has also written five novels. Storm Jameson praised his first novel, Gone to Timbuctoo, as "an unusually good first novel, an exciting story, and a splendid setting in French West Africa. The writing is sharp and witty."Malcolm Muggeridge said, "This is an exceptionally brilliant first novel - exciting, wryly funny and perceptive."