In 1943, Boldrini joined the then clandestine Italian Communist Party and has been one of the main promoters of the Resistance in Romagna.

[1] During the Resistance, Boldrini was the National Liberation Committee's reference man of Ravenna and leader of the 28th Garibaldi Brigade entitled to the partisan "Mario Gordini".

[1] During the Nazi-Fascist occupation, Boldrini was always at the forefront during the liberation missions in Romagna and was nicknamed Bulow, an homage to Prussian general Friedrich Wilhelm Freiherr von Bülow.

[2] In 1945, some days immediately after the end of the war, his Brigade was still active in an area where had place a massacre of over 130 surrendered RSI soldiers and some former fascist civilians in Codevigo: in the last years he was indicated by revisionist researchers as the principal instigator of the crime,[3] but in early post-war investigations Boldrini had already been acquitted of the same charges before trial, as it was demonstrated that the massacre was carried "... outside and against his orders and without his knowledge ...", and it's testified that he was elsewhere in the days of the massacre.

[4] Boldrini has embodied the ethical and political motives behind the struggle of the Italian Resistance, becoming one of the most authoritative and credible representatives at the institutional level: after being elected to the Constituent Assembly, Boldrini became the first President of the National Association of Italian Partisans, holding this office from 1947 to 2006.