This essay wants to reconstruct the role of Livio Paladin as a Constitutional Judge. It first outlines the historical and political context surrounding the appointment of the very young constitutional law scholar by the then President of the Republic Giovanni Leone. The author identifies this phase as one of «judicial activism». Through the analysis of Paladin's work, the essay tries to isolate his contribution to the case law of the Italian Constitutional, with particular attention to the decisions that he directly authored. In its last part, the essay reflects on the influence of Paladin's experience as a Constitutional Judge on his further scientific production, underlining his particular sensitivity for the study of the historical context in which Constitutions are formed and they live and develop as «living organisms».