The author describes the main steps of the socialist leader's experience within the trade union, which correspond to some of the most important moments of the history of the Italian General Confederation of Labour (CGIL). Piero Boni was definitely one of the leading figures of this trade union until 1977, when he decided to resign from the office of Deputy Secretary General. In fact, after the election of Bettino Craxi as Secretary of the Italian Socialist Party (PSI), Boni did not jump on the bandwagon and thus remained isolated within the trade union's socialist wing. In particular, the article deals with: 1. Boni's fight for the renewal of the contractual action, and for the elimination of the trade union's oligarchic structure; 2. his commitment to the autonomy of the trade union from the political party it referred to; this commitment gathered momentum during the Hungarian Revolution and in the declaration of incompatibility of any political office with the appointment as unionist; 3. his participation in the debate on the disaffiliation of cgil from WFTU; 4. his passionate fight for trade union unity; 5. his role as a researcher in history of trade unionism, and as a promoter of cultural initiatives when he took office as President of Fondazione Giacomo Brodolini.