Lewis was born in Forty Hill, Enfield, Middlesex, a suburb of London, and attended Enfield Grammar School.

Lewis served in World War II and wrote an account of his experiences during the Allied occupation of Italy, titled Naples '44. Shortly after the war he produced volumes about Burma, titled Golden Earth, and French Indochina, titled A Dragon Apparent. His intrepid boots-on-the-ground view of Vietnam under French colonial domination, without being itself a political rant, gives context to any discussion of the American experience in that battered and subjugated part of the world.

Lewis was fascinated by cultures which were little touched by the modern world. This was reflected in his books on travels in Indonesia, An Empire of the East, and among the tribal peoples of India, A Goddess in the Stones.

Lewis's first wife, Ernestina, was a Swiss-Sicilian aristocrat, and Sicilian life, including the Mafia, was another of his major themes, reflected in The Honoured Society and In Sicily. His treatment of the Mafia was not sensationalist but based on an acute understanding of Sicilian society and a deep sympathy with the sufferings of the Sicilian people, without losing sight of the horrors inflicted by the organisation.

Another major concern of Lewis's was the impact of missionary activity on tribal societies in Latin America and elsewhere. He was hostile to the activities of missionaries, especially American evangelicals. This is covered in the volume, Among the Missionaries and several shorter pieces. He frequently said that he regarded his life's major achievement as the worldwide reaction to writing on tribal societies in South America. In 1968, his article "Genocide in Brazil" published in the Sunday Times created such an outcry that it led to the creation of the organisation Survival International, dedicated to the protection of first peoples around the world.

Lewis wrote several volumes of autobiography, again concerned primarily with his observations of the many places in which he lived at various times, which included St Catherine's Island in South Wales near Tenby, the Bloomsbury district of London during World War II, Nicaragua, a Spanish fishing village, and a village near Rome.

Lewis also wrote twelve novels. Some of these enjoyed significant success at the time of publication, but his reputation rests mainly on his travel writing.

He died in Saffron Walden, Essex, survived by his third wife, Lesley, and their son, Gawaine, and two daughters, Kiki and Samara, and by a son, Gareth, and daughter, Karen, from his second marriage with Hester, and by a son, Ito, from his first marriage.

Novels

• Samara (Cape 1949)
• Within the Labyrinth (Cape 1950; US: 1986 Carroll)
• A Single Pilgrim (Cape 1953; US: 1953 Rinehart)
• The Day of the Fox (Cape 1955; US: 1955 Rinehart)
• The Volcanoes Above Us (Cape 1957; US: 1957 Pantheon, not dated)
• Darkness Visible (Cape 1960; US: 1960 Pantheon)
• The Tenth Year of the Ship (Collins 1962; US: 1962 Harcourt)
• A Small War Made to Order (Collins 1966; US: 1966 Brace)
• Every Man's Brother (Heinemann 1967; US: 1968 Morrow)
• Flight from a Dark Equator (Collins 1972; US: 1972 Putnam)
• The Sicilian Specialist (Random 1974; UK: 1975 Collins)
• The German Company (Collins 1979)
• The Cuban Passage (Collins 1982; US: 1982 Pantheon)
• A Suitable Case for Corruption (Hamilton 1984; US: 1984 Pantheon, as The Man in the Middle)
• The March of the Long Shadows (Secker 1987)

Travel & Miscellaneous

• Spanish Adventure (1935, later disowned)
• Sand and Sea in Arabia (Routledge 1938)
• A Dragon Apparent - Travels in Indo-China (Cape 1951; US: 1951 Scribner's)
• Golden Earth - Travels in Burma (Cape 1952; US: 1952 Scribner's)
• The Changing Sky The Travels of a Novelist (Cape 1959; US: 1959 Pantheon)
• The Honoured Society - The Mafia Conspiracy Observed (Collins 1964; US: 1964 Putnam's; London: Eland, 2003)
• Naples '44 (Collins 1978; US: 1978 Pantheon)
• Voices of the Old Sea (Hamilton 1984; US: 1985 Viking)
• Jackdaw Cake (Hamilton 1985)
• A View of the World (Eland 1986)
• The Missionaries (Secker 1988; US: 1988 McGraw)
• To Run Across the Sea (Cape 1989)
• A Goddess in the Stones - Travels in India (Cape 1991; US: 1992 Holt)
• An Empire of the East Travels in Indonesia (Cape 1993; US: 1993 Holt)
• I Came I Saw (Picador 1994) - extended issue of 'Jackdaw cake'
• The World The World (Cape 1996; US: 1997 Holt)
• The Happy Ant-Heap (Cape 1998)
• A Voyage by Dhow (and other pieces) (Cape2001)
• The Tomb in Seville (Cape 2003)