He was undergoing treatment at Ramathibodi Hospital.
A royal-sponsored bathing rite will be held on Wednesday at 5pm at the Marble Temple.
Sawad was appointed to the Privy Council in 2002, culminating a long career in public service.
Following his graduation in structural engineering from the Massachusetts Institute of Technology, he entered the civil service with the Royal Irrigation Department in 1962.
He rose to become the director-general of the department in 1992, before retiring in 1995.
He continued to be active and served as a justice at the Supreme Administrative Court from 2000-02.
Born in 1934 to a prominent family in Pattani, he was the seventh son among 10 children. He father was civil servant Khunthamrongpanpakdee and his mother was Soithong Wattanayagorn nee Khananurak.
He attended a local elementary school and received his secondary education at Bangkok Christian College before going to Australia and the United States for further studies.
He is survived by his wife Khunying Panjit and a son.