He served as the 39th minister of foreign affairs of Thailand from 11 March 2005 until the military coup d'état on 19 September 2006.

[1][2][3] While foreign minister, Kantathi enhanced Thailand's diplomatic role in the Association of Southeast Asian Nations (ASEAN), and in the world at large.

He had been to the DPRK several times and has worked closely with the then U.S. Secretary of State Condoleezza Rice, the People's Republic of China's Foreign Minister Li Zhaoxing, and the Republic of Korea's Foreign Minister Ban Ki-moon, with the goal of maintaining peace and security on the Korean Peninsula.

Kantathi is presently a member of the advisory board of the RAND Corporation Center for Asia Pacific Policy.

[9][10] Kantathi also served as special adviser to Her Royal Highness Princess Chulabhorn Walailak of Thailand.

In this role, he accompanied Her Royal Highness on trips to numerous countries pertaining to medical research, the environment, and various other international activities.