Lawyers who are considered in this paper are called in Usa cause lawyers, in France and Italy activist advocates. Their peculiarity lies in their commitment in the defense of political activists charged in trials and in the defense of victims of any violence and discrimination. The topic of causelawyering has been studied by American and French sociologists but it is quite neglected by historians. This paper aims to start a historical research by considering in a comparative perspective a group of French and Italian lawyers belonging to different generations who practiced along the XXth century. Most of them were political activists and their commitment in acting the legal profession made them witnesses of the Twentieth century. In this perspective this paper focuses lawyers of both countries engaged in the defense of Communist activists, French advocates who defended Algerian nationalists, Italian lawyers who represented in court resistant fighters accused after the Second world war, and Italian Red brigades imprisoned in the Seventies and Eighties. In the conclusion of the paper, the opening of a new research field is suggested to study lawyers commitment in the XXth century, that of trials against health and environment crimes.