Jagath was born in Colombo Sri Lanka. He is the only son of Mr KPW Ramanayake and Mrs Nanda Ramanayke. Jagath has three siblings, one older sister Dr Asoka and two younger sisters Dr Enoka Wagaarachchi and Dharshika. His mother was a curriculum developer, and his father a businessman. Jagath’s parents were the pioneering Japanese car exporters in Sri Lanka just after economical revolution started in SL in 1977. Later they expanded their business interests in SL as well as overseas.
Jagath attended Nalanda College, Colombo. He completed his tertiary education in Japan where he obtained B.Sc in business from The University of Yokohama "Kanto Gakuin University" in 1990. Later he completed an MBA at Tokyo University of Information Sciences. His research thesis was on Transferability of Japanese Management to Asia.
In 1996 Jagath married Miss Samantha Subasinghe, a solicitor. Jagath and Samantha have four children. Samantha now works as a director for the RAMA DBK in its sales division.
Jagath is keen sportsman. He captained the Rugby 1st XV – Nalanda College (1985) and “A – Division Rugby – Peterson Club” (1987-1988). He is team coach for "ALHI FOOTBALL CLUB" – Yokohama ( 2005 to date).