McKern was the son of James Gordon McKern (1888–1975) a mining engineer, geologist and petrologist who became a technical executive with the petroleum company Mobil and Edith Mary Hamlet (1890–1967), daughter of William Mogford Hamlet. McKern was born in Mosman, New South Wales and educated at Newington College (1931–1935).
In 1957 he completed a Master of Science degree, by thesis, at the University of New South Wales.
In the Leaving Certificate Examination he was awarded First-Class Honours in Chemistry and Geology. McKern received a Diploma in Chemistry from the Sydney Technical College in 1942, while studying physiology, microbiology and botany. McKern worked from 1936 until 1945 in analytical and organic chemistry in the Parramatta chemical laboratory of Meggitt Limited, and during that time was promoted to Assistant Chemist.
He was appointed Deputy Director of the Museum in 1960 and retired in 1977.
Fellow - Royal Australian Chemical Institute (1957)
President - UNSW Chemical Society (1960–1971)
Recipient - Royal Society Medal (1968)
President - Royal Society of New South Wales (1970).
