Bordet was born in Soignies, Belgium, and graduated in medicine from Brussels University in 1892. In 1894 joined the Pasteur Institute, Paris, where he worked under the bacteriologist Elie Metchnikoff. In collaboration with Octave Gengou, Bordet discovered that in an immunized animal the antibodies produced by the immune response work in conjunction with another component of blood (which Bordet termed ‘alexin’ but which is now called ‘complement’) to destroy foreign cells that invade the body. This component, Bordet found, was present in both immunized and nonimmunized animals and was destroyed by heating to over 55°C. This work formed the basis of the complement-fixation test, a particularly sensitive means of detecting the presence of any specific type of cell or its specific antibody. A notable application of this was the test to detect syphilis devised by August von Wasserman.

In 1901 Bordet left Paris to found and direct the Pasteur Institute in Brussels and in 1907 he was appointed professor of pathology and bacteriology at Brussels University. In 1906 Bordet isolated the bacterium responsible for whooping cough, which is named after him: Bordetella (Haemophilus) pertussis. For his discovery of complement and other contributions to medicine, he was awarded the 1919 Nobel Prize in physiology or medicine.