This article examines the relationship between legality and legitimacy in postcolonial constitution-making, focusing on Singapore's two stages of sovereignty transfer from colonial rule to independent statehood: its decolonisation from Britain in 1963, achieved through merger with Malaysia, and its separation from Malaysia in 1965. The article shows how different forms of legitimacy were established and sustained during these transitions. The first independence was characterised by legal continuity and political legitimacy, solidified through peaceful negotiations and the strategic use of a 1962 referendum that helped mitigate internal opposition. By contrast, the second independence in 1965 was a ‘legal revolution’, as neither the Malaysian Federal Constitution nor the State of Singapore Constitution 1963 provided for secession and the People's Action Party (PAP) government lacked an explicit public mandate to negotiate the secession. This break in legal continuity required new sources of (revolutionary) legitimacy, which the PAP government secured through subsequent electoral dominance, constitutional consolidation, and political manoeuvres. This article underscores the fact that legitimacy in making, amending, and consolidating constitutions is inherently transient and unstable, requiring continuous renewal through various political and legal mechanisms.