De Mel and Don Anurasiri were retained from the previous selection panel and will be joined by Mahes Goonathilake and Ranjith Madurasinghe in the new committee.
Amal Silva and Shabir Asgerally were dropped from the panel.
"I have considered their wide experience as former cricketers," sports minister Gamini Lokuge told AFP after naming the new committee.
Goonathilake kept wicket in Sri Lanka's inaugural Test against England in 1982 before joining a rebel tour of South Africa later that year.
Madurasinghe, a former off spinner who made his Test debut at Lord's in 1988, played three Tests. He was recalled for a second term as selector.
De Mel was re-appointed by the sports minister even though his nomination was opposed by the incumbent administration of Sri Lanka Cricket, the governing body of the sport in the island nation.
The new panel's first task will be to pick a squad for the inaugural Twenty20 world championships in South Africa in September.
Sri Lanka are also due to tour Australia for two Tests in November.