A1.62km section of the 4km runway had been closed since June 11 for repairs. The runway's closure had resulted in heavy congestion at the two-runway airport.
The runway repairs were completed today, ten days ahead of the Aug 9 deadline, the AOT chief said.
Mr Anirut said he believed the return to full service will help reduce and eventually eliminate flight delays.
During the first week of repairs on the eastern runway, some 104 flights were delayed daily, with an average delay of 20-30 minutes for each flight.
Since reopening today, the eastern runway is now capable of servicing 76 flights per hour as it used to be. It can accommodate all types of aircraft.