Fleischmann was born in Karlovy Vary, Czechoslovakia, in 1927. His father was a wealthy lawyer and his mother the daughter of a high-ranking Austrian civil officer. Since his father was of Jewish heritage, Fleischmann's family moved to the Netherlands, and then to England in 1938, to avoid Nazi persecution. His father died of the complications of injuries received in a Nazi prison, after which Fleischmann lived for a period with his mother in a leased cottage in Rustington, Sussex. His early education was obtained at Worthing High School for Boys. After serving in the Czech Airforce Training Unit during the war, he moved to London to study for undergraduate and postgraduate degrees in chemistry at Imperial College London. His PhD was awarded in 1951, under the supervision of Professor Herrington, for his thesis on the diffusion of electrogenerated hydrogen through palladium foils. He met Sheila, his future wife, as a student and remained married to her for 62 years.