Fleming was born in Mayfair, London, to Valentine Fleming, an MP, and his wife Evelyn Ste Croix Fleming. Ian was the younger brother of travel writer Peter Fleming and the older brother of Michael and Richard Fleming. He also had an illegitimate half-sister, the cellist Amaryllis Fleming.
In 1914 Fleming attended Durnford School, a preparatory school on the Isle of Purbeck in Dorset. In 1921 Fleming enrolled at Eton College. Although not a high achiever academically, he excelled at athletics and held the title of Victor Ludorum ("Winner of the Games") for two years between 1925 and 1927. His lifestyle at Eton brought him into conflict with his housemaster, E. V. Slater, who disapproved of Fleming's attitude, his hair oil, his ownership of a car and his relations with women. Slater persuaded Fleming's mother to remove him from Eton a term early for a crammer course to gain entry to the Royal Military College at Sandhurst.
In 1927, to prepare Fleming for possible entry into the Foreign Office, his mother sent him to the Tennerhof in Kitzbühel, Austria, a small private school run by the Adlerian disciple and former British spy Ernan Forbes Dennis and his novelist wife, Phyllis Bottome. After improving his language skills there, he studied briefly at Munich University and the University of Geneva.
The author Geoffrey Jenkins worked with Fleming on a James Bond story idea between 1957 and 1964. After Fleming's death, Jenkins was commissioned by Bond publishers Glidrose Productions to write a Bond novel, Per Fine Ounce, into a novel, but it was never published.
In 1960, Fleming was commissioned by the Kuwait Oil Company to write a book on the country and its oil industry. The typescript is entitled State of Excitement: Impressions of Kuwait but it was never published due to disapproval by the Kuwaiti Government. According to Fleming: "The Oil Company expressed approval of the book but felt it their duty to submit the typescript to members of the Kuwait Government for their approval. The Sheikhs concerned found unpalatable certain mild comments and criticisms and particularly the passages referring to the adventurous past of the country which now wishes to be 'civilised' in every respect and forget its romantic origins."