Banpu also recently secured $US2 billion worth of loans from Thai and foreign banks to finance the transaction.
The takeover remains subject to Foreign Investment Review Board approval.
Banpu withdrew its FIRB application in late July because of the pending federal election.
Banpu’s takeover offer at $A6.20 per share on July 5 was made at a 40% premium to the closing price of Centennial shares on the previous trading day.
The Thai company first bought a 14.89% stake of Centennial in the first week of May and bought another 5% stake in mid-June.
Centennial is one of the few remaining independent coal producers in Australia.
Shares in Centennial last traded at $5.98.