Fleming je rođen na farmi u Lochfieldu blizu Darvela u East Ayrshire, Škotska, a školovan je na akademiji u Kilmanrocku. Poslije je studirao u St. Mary's Hospitalu u Londonu do početka Prvog Svjetskog Rata.
Sir AlexanderFleming FRS FRSE FRCS [2 ] (6 August 1881 – 11 March 1955) was a Scottish physician and microbiologist, best known for discovering the world's first broadly effective antibiotic substance, which he named penicillin.