ABSTRACT Scholars of Thai politics have paid significant attention to the role played by signs and symbols in Thailand, especially as interpretations of the political struggle after the 1932 Revolution. Some scholars believe that the People’s Party successfully used constitutionalism to counter royalism, but critics contend that the Party failed in its quest to curb the royalists because it appropriated royal sources of legitimacy in its efforts to promote the constitution. This article proposes that even though the selection of 10 December as Constitution Day was indeed a compromise on symbolism with the royalists, the Party – and especially Prime Minister Plaek Phibunsongkhram (Phibun) – did confront the royalists by later honouring 24 June as National Day. This article examines the political meanings of Thailand’s first National Day celebrations on 24 June 1939, which scholars often neglect, and argues that the Party symbolically turned it against the absolute monarchy by using the day’s festivities to highlight and legitimise the achievements of the post-absolutist constitutional regime without involving any royal symbols. In other words, Thailand’s National Day in 1939 was constructed by the Party as a site of legitimacy that was independent of royal influence and free of royal legitimation.