Phan Wannamethee (born 30 January 1924) is a Thai diplomat who served as the sixth secretary-general of ASEAN between 1984 and 1986.
Phan Wannamethee graduated from Oberlin College with a bachelor's degree in history and a master's degree in international relations from the University of California, Berkeley.
As Secretary-General of the Association of Southeast Asian Nations (ASEAN), he played an important role and is behind the draft of the Treaty of Amity and Cooperation in Southeast Asia.
Phan was former Secretary-General of the Thai Red Cross Society until resigning from the position in 2021.