Born 1857 in Mantua; died 1927 in Rome. Figure in the Italian workers’ movement. A journalist by profession.
Lazzari helped found the Italian Workers’ Party in 1882 and the Italian Socialist Party (ISP) in 1892. In the early 20th century, when intraparty strife within the ISP intensified, he was one of the leaders of the left wing; from 1912 to 1919 he was secretary of the party. He carried on the struggle against reformists; however, he strove to avoid a schism in the ISP by adopting centrist positions. During World War I he proposed the pacifist slogan “no participation and no sabotage,” which became the official platform of the ISP. He was a participant in the Zimmerwald (1915) and Kienthal (1916) conferences. He wanted the ISP to join the Comintern and became the leader of the group of Comintern supporters in the ISP (the Third Internationalists), but he did not join the Italian Communist Party. He served as a deputy to parliament from 1919 to 1926. During the period of fascist rule he was active in the antifascist opposition.