Phan Wannamethee (born 30 January 1923) 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.^[1]

Phan was former Secretary-General of the Thai Red Cross Society until resigning from the position in 2021.^[2]

• Knight Grand Cross (First Class) of The Most Admirable Order of the Direkgunabhorn^[3]