This is believed to be the first step for him to be named chairman of the 66% state-owned energy giant, as protocols dictate the chairman of the board must be selected from directors.
The board resolved at its meeting today to replace Panpree Bahiddha-Nukara with Mr Piyasvasti.
Mr Pranpree stepped down as independent director and chairman of the board on June 15, following the junta's plan to purge state enterprises' boards of politicians and their cronies and fill them with competent persons with knowledge in the field.
Mr Piyasvasti was the energy minister in the appointed government following the 2006 coup.
He was formerly secretary-general of the Thai National Energy Policy Office, chairman of Kasikorn Asset Management and chairman of Panel of Advisors for CEO of Kasikornbank.
He was also president of Thai Airways International between October 2009 and June 2012. He is currently chairman of the Energy for Environment Foundation, a non-profit organisation undertaking renewable energy and energy-efficiency projects.
His wife is a former Democrat party-list MP.
At today's meeting, PTT's board also resolved to name Kurujit Nakornthap as director.
Mr Kurujit is deputy permanent secretary of the Energy Ministry.
Gen Paibool Khumchaya, Pornchai Rujiprapa, Kittipong Kittiyarak and Nuntawan Sakuntanaga were also named independent directors.
Gen Paibool is one of the National Council for Peace and Order's members.
Mr Pornchai was a former chairman of the board at Electricity Generating Authority of Thailand in 2012 and 2013 during both the Abhisit Vejjajiva and Yingluck Shinawatra governments.
Mr Kittipong was justice permanent secretary and leader of the Reform Now Network.
Mrs Nuntawan is director-general of the Department of International Trade Promotion.
PTT also told the Stock Exchange of Thailand four more of its independent directors will resign on June 30.
They are Thosaporn Sirisumphand, Sihasak Phuangketkeow, Boonsom Lerdhirunwong and Insorn Buakeow.
On June 16, Waroonthep Watcharaporn, an independent director, also resigned, followed by Athapol Yaisawang, also an independent director, a day later.