Ranatunga's decision came three days after Sri Lanka's tour of India where they lost a three-Test series 2-0. They had also crashed to a 6-1 defeat to India in a preceding seven-match One-day series.
Ranatunga was heading a committee which involves all past captains.
"As a person who loves cricket in Sri Lanka I worked hard to execute my responsibility as the chairman of the committee. It is regretful that the expected outcome was not there.
"Under these circumstances I am left with no alternative but to resign," Ranatunga wrote in a letter to Sri Lanka Cricket (SLC).
"There were a few things that I wasn't at all happy with during my association with SLC and I just waited till the team returned from India to hand over my resignation," Ranatunga told AFP.
Although he didn't outline details of what made him unhappy, it is believed that Ranatunga and his committee had differences of opinion with SLC Chairman Jayantha Dharmadasa.
Ranatunga's committee was responsible for appointing former Australian Test cricketer Tom Moody as coach of the national team in place of his compatriot John Dyson.