Hugh John Forster Cairns was born on November 21, 1922, in Oxford, England. He received a B.A in 1943, followed by a B.M and B.Ch. in 1946 and a D.M. degree in medicine in 1952 from Oxford University. Between 1950 and 1951, he worked in Melbourne, Australia a virologist at the Hall Institute. In 1952 he was called back by the British Colonial Office to work at the Virus Research Institute in Entebbe, Uganda. Cairns returned to Australia in 1955 to take a position at the Australian National University at Canberra until 1963. During that time, he spent two sabbaticals in the United States: he worked in 1957 at the California Institute of Technology in Renato Dulbecco's laboratory, and in 1960 at Cold Spring Harbor Laboratory with Al Hershey.

At Cold Spring Harbor, Cairns studied of DNA replication, using a technique he initiated, called molecular autoradiography. Using replicating DNA molecules from E. coli, he showed that the chromosome was shaped like a circle, 700-900 microns long, and that DNA replication produced a fork as the helix separated and each strand was duplicated. Cairns became the Director of Cold Spring Harbor Laboratory and served from 1963 to 1968, overseeing its creation by amalgamation of the Biological Laboratory with the Carnegie Institution's Department of Genetics.

Cairns maintained the financial integrity of Cold Spring Harbor at a difficult time in the Laboratory's history. In 1968, he chose to step down as director so that he could focus on research. He remained a staff member at Cold Spring Harbor until 1973 when he was appointed Head of the Mill Hill Laboratories of the Imperial Cancer Research Fund, London. Cairns's research at Mill Hill focused on DNA mutagenic agents and the role of certain chemicals in cancer production. Through his research on E. coli, he demonstrated that there is a system to repair DNA mutations.

In the fall of 1980 Cairns was appointed Professor of Microbiology at the Harvard School of Public Health, from which he retired in 1991. Throughout his life-long research, Cairns elucidated the complex process of DNA replication in living cells.

Cairns has been honored with various wards throughout his scientific career. In 1967, he became a Fellow of the American Academy of Arts and Sciences and in 1974, he was made a fellow of the Royal Society. He became a MacArthur Foundation Fellow in 1981. Between 1980 and 1982, Cairns served as the vice-chairman of the National Academy Committee on "Diet, Nutrition, and Cancer."

In addition to his scientific publications, Cairns published a book in 1978 for non-specialists, Cancer, Science and Society. In 1997, Cairns wrote a series of essays, Matters of Life and Death: Perspectives on Public Health, Molecular Biology, Cancer, and the Prospects for the Human Race.