[1] Jayathilake was educated at the Royal College, Colombo,[2] where he won the De Abrew Memorial Prize.
He then went on to graduate with First Class Honours from the University of Ceylon with a BSc in engineering and soon after receiving the Ceylon Government University Scholarship (1960), for best performance at the engineering degree examination to study for a postgraduate Diploma of Imperial College (1963) in thermal process engineering, where he won the Unwin Memorial Scholarship.
In 1966 he gained a PhD from the Imperial College, London for research in heat transfer.
Upon retirement he was made an emeritus professor, and he is a fellow of the Institute of Engineers of Sri Lanka.
Later he was the chancellor of Wayamba University of Sri Lanka and chairman of the National Institute of Business Management.