Ambassador Piamsak was born in 1950 in Bangkok, Thailand. He was educated at Chulalongkorn University in Thailand and Wayne State University in the United States.

His professional career is as follows:

• 1977–1980: Attaché, Department of Economic Affairs, Ministry of Foreign Affairs, Thailand
• 1981–1984: Second Secretary, Royal Thai Embassy, Singapore
• 1985–1987: First Secretary, Department of ASEAN Affairs, Ministry of Foreign Affairs, Thailand
• 1988–1991: Counsellor, Permanent Mission of Thailand to the United Nations New York
• 1992–1994: Director, North American Division, Department of American and South Pacific Affairs, Ministry of Foreign Affairs, Thailand
• 1995–1999: Minister, Deputy Permanent Representative, Mission of Thailand to the World Trade Organization, Geneva
• 1999: Deputy Director-General, Department of ASEAN Affairs, Ministry of Foreign Affairs, Thailand
• 2000–2001: Deputy Director-General, Department of European Affairs, Ministry of Foreign Affairs, Thailand
• 2002: Deputy Executive Director, Asia-Pacific Economic Cooperation Secretariat
• 2003: Executive Director, Asia-Pacific Economic Cooperation Secretariat