Hawthorne was born in Newcastle-upon-Tyne, England, the son of a civil engineer from Belfast. He had two younger brothers, John and Edward. He was educated at Westminster School, London, then read mathematics and engineering at Trinity College, Cambridge, graduating in 1934 with a double first. He spent two years as a graduate apprentice with Babcock & Wilcox Ltd, then went to the Massachusetts Institute of Technology in Cambridge, MA, where his research on laminar and turbulent flames earned him a ScD two years later. In 1939 he married Barbara Runkle, and they had one son and two daughters. After MIT, he returned to Babcock & Wilcox. In 1940, he joined the Royal Aircraft Establishment at Farnborough. He was seconded from there to Power Jets Ltd at Lutterworth, where he worked with Frank Whittle on combustion chamber development for the jet engine. Building on his work on the mixing of fuel and air in flames at MIT, he derived the mixture for fast combustion; the chambers produced by his team were used in the first British jet aircraft. In 1941, he returned to Farnborough as head of the newly formed Gas Turbine Division and in 1944 he was sent for a time to Washington to work with the British Air Commission. In 1945, he became Deputy Director of Engine Research in the British Ministry of Supply before returning to America a year later as an Associate Professor of Engineering at MIT. He was appointed George Westinghouse Professor of Mechanical Engineering there at the age of 35, and in 1951 returned to Cambridge, UK as the first Hopkinson and Imperial Chemical Industries Professor of Applied Thermodynamics. Hawthorne's most outstanding work at Cambridge was in the understanding of loss mechanisms in turbomachinery, and during his time as Head of Department he and Professor John Horlock established the Turbomachinery Laboratory. The oil shortage following the Suez Crisis and Hawthorne's interest in energy matters led to his invention and development of Dracone flexible barges for transporting oil, fresh water, or other liquids. Hawthorne was active on many committees and advisory bodies concerned with energy matters, in particular the Advisory Council on Energy Conservation, of which he was chairman from its inception in 1974. Hawthorne was elected to the fellowship of the Royal Society in 1955, and was knighted in 1970. He became Head of the Department of Engineering in Cambridge in 1968 and was appointed Master of Churchill College, Cambridge in the same year. President of the Pentacle Club from 1970–1990, Hawthorne was well known for performing magic, and is remembered to this day by the kitchen staff at Churchill College as 'the man who made cheese rolls come out from behind his ears'.
