The puzzle that drives this study is why Thailand pursued a proactive foreign policy towards greater powers during the Second World War. The main literature on Thai foreign policy-making generally suggests that Thailand is traditionally passive vis-à-vis greater powers. Oftentimes, it is believed that the fate of Thailand is subjected to the dictate of great powers. The empirical cases of Thailand during the Second World War suggest otherwise. How could a conventional understanding of Thai foreign policy make sense of Thailand’s war against France in 1940-41? Similarly, how could one understand Thailand’s defiant behaviours vis-à-vis Japan in 1941-44 despite the latter’s greater military capabilities and influence? This thesis employs the approaches of ontological security and status concern to interpret Thai proactive behaviours during the wartime period. It argues that concerns for status and recognition from the great powers were the primary motivations of Thailand’s proactive behaviours. In order to discern material and ideational motives of the Thai foreign policy-makers, this research heavily relies on archival research and utilises documents which were formerly considered to be classified. This methodological quest is to establish and enhance the credibility of the argument presented in the study.