This paper sees the core problem faced by the Provisional Government of the Republic of Korea as one of legitimacy and attempts to examine the National Representative Conference held in Shanghai in 1923 in consideration of the controversy over the Provisional Government’s legitimacy. Activists of the Korean independence movement founded the Provisional Government as a government in exile amidst this vacuum of legitimate authority, in line with the spirit of the March First Movement of 1919. However, the Provisional Government proved unable to establish supreme authority. Efforts to build the legitimacy of the Provisional Government culminated in the organization of the National Representative Conference (NRC), which brought together various independence movement activists. During the NRC, the legitimacy of the Provisional Government’s supreme authority was approached from four different perspectives: historical, constitutional, democratic, and value-oriented.