Born in Budapest, Hungary, son of Desiderius (Deszo) and Anna Elek. Educated at the Lutheran High School.

Studied medicine at St George's; qualified in 1939. Assistant bacteriologist at the pathology department in 1940; Laking-Dakin fellowship in pathology 1942-1943. Obtained a PhD in microbiology. Appointed consultant bacteriologist in 1948. Fulbright fellowship in 1956 in Harvard Medical School, USA. Chair of medical microbiology at St George's in 1957. Worked to establish immunology as a discipline at St George's, although this was only achieved after his retirement, in 1978; he endowed an undergraduate Elek prize in the subject. Persuaded the Public Health Laboratory Service to establish a Public Health Laboratory to join St George's microbiology department in Tooting in 1966. The new microbiology laboratories were named after him in 1984.

Clinical pathologist to the Maida Vale Hospital for Nervous Diseases 1946-1947. The first editor of the Journal of Medical Microbiology after persuading the Pathological Society to split the Journal of Pathology and Bacteriology into two separate journals in 1968.

Researched and published on immunology, microbiology and virology, including serological reactions of staphylococcus aureus and diphtheria toxins with Emmanuel Levy; the 'Elek plate' was used for testing for diphtheria bacilli. His research interests also included leprosy and resistotyping, a method for distinguishing between different strains of bacterial species. With his colleagues he recognized a new disease caused by herpes simplex virus infection in the hands of nurses, preventable by wearing of gloves.

Married Sarah Joanna Hall in 1947; they had three daughters. Retired in 1973.