Subjects he explored in his travel writing include life in Naples during the Allied liberation of Italy (Naples '44); Vietnam and French colonial Indochina (A Dragon Apparent); Indonesia (An Empire of the East); Burma (Golden Earth); tribal peoples of India (A Goddess in the Stones); Sicily and the Mafia (The Honoured Society and In Sicily); and the destruction caused by Christian missionaries in Latin America and elsewhere (The Missionaries).

His newspaper article entitled "Genocide in Brazil" (1969)[1] prompted the creation of Survival International—an organisation dedicated to the protection of indigenous peoples around the world.

[4] A clever child, Lewis was bullied by other children, and sent by his parents to live for a couple of years with three deeply religious "half-mad aunts" in Wales.

[5] Having been educated at Enfield Grammar School, as a young man, Lewis tried a variety of ways to make a living in the Great Depression of the 1930s, including self-employed wedding photographer, auctioneer, umbrella wholesaler and briefly a motorcycle racer at Harringay Stadium and White City.

[6] Lewis's different books give varying accounts of his British Army service in World War II.

He frequently said that he regarded his life's major achievement as the worldwide reaction to writing on tribal societies in South America.

Lewis wrote several volumes of autobiography, again concerned primarily with his observations of the many places in which he lived at various times, including St Catherine's Island in South Wales near Tenby, the Bloomsbury district of London during World War II, Nicaragua, a Spanish fishing village (Voices of the Old Sea),[2] and a village near Rome.

In Castro di Volsci doctors treated 300 victims of rape, and at Ceccano the British have been forced to build a guarded camp to protect the Italian women.Lewis's first wife, Ernestina Corvaja,[2] was a Swiss-Sicilian.

[7] Sicilian life, including the role of the Mafia, was a major theme, which he explored in The Honoured Society (1964) and In Sicily (2000).