His father, an ardent Socialist, was a blacksmith; his mother was a teacher. Mussolini taught briefly and lived (1902–4) in Switzerland to avoid military service. He achieved national prominence for his opposition to the Libyan War (1911–12) and, as leader of the revolutionary left of the Socialist party, became editor of the Socialist daily Avanti (1913). Soon after World War I began, Mussolini abruptly turned nationalist and joined the pro-Allied interventionists. The Socialist party, which opposed all participation in nationalist wars, expelled him. He then founded his own daily, the Popolo d'Italia, which was subsidized by the French to encourage Italy's entry into the war on the side of the Allies. He joined (1915) the army and attained the rank of corporal.

In the troubled postwar period Mussolini organized his followers, mostly war veterans, in the Fasci di combattimento, which advocated aggressive nationalism, violently opposed the Communists and Socialists, and dressed in black shirts like the followers of D'Annunzio. Amid strikes, social unrest, and parliamentary breakdown, Mussolini preached forcible restoration of order and practiced terrorism with armed groups. In 1921 he was elected to parliament and the National Fascist party (see fascism) was officially organized. Backed by nationalists and propertied interests, in Oct., 1922, Mussolini sent the Fascists to march on Rome. King Victor Emmanuel III permitted them to enter the city and called on Mussolini, who had remained in Milan, to form a cabinet.

As the new premier, he gradually transformed the government into a dictatorship. In 1924 the Socialist deputy Matteotti was murdered. Opposition was put down by an efficient secret police and the Fascist party militia, and the press was regimented. Parliamentary government ended in 1928, and the state economy was reorganized along the lines of the Fascist corporative state. Conflict between church and state was ended by the Lateran Treaty (1929).

Mussolini was called Duce [leader] by his followers; his official title was head of the government, and he held, besides the premiership, as many portfolios as he saw fit. His ambition to restore ancient greatness found expression in grandiloquent slogans and speeches and in the erection of monumental buildings. The encouragement he gave to the already high Italian birth rate, his imperialistic designs, and his incitement of extreme nationalist groups created an explosive situation.

Mussolini was at first cool to Adolf Hitler and opposed his designs on Austria. However, Mussolini's diplomatic isolation after his attack (1935) on Ethiopia led to a rapprochement with Germany. In 1936, Hitler and Mussolini aided Francisco Franco in the Spanish Civil War; the Rome-Berlin Axis was strengthened by a formal alliance (1939), which Mussolini's son-in-law and foreign minister, Galeazzo Ciano, helped to create.

In 1938, Mussolini allowed Hitler to annex Austria and helped bring about the Munich Pact; in Apr., 1939, he ordered the Italian occupation of Albania. Under German pressure, he inaugurated an anti-Semitic policy in Italy, which found little popular response. The Ethiopian and Spanish wars had diminished the Duce's popularity, and he did not enter World War II until France was falling in June, 1940.

The failure of Italian arms in Greece and Africa and the imminent invasion by the Allies of the Italian mainland at last caused a rebellion within the Fascist party. In July, 1943, the Fascist grand council refused to support his policy—dictated by Hitler—and the king dismissed him and had him placed under arrest. He was freed two months later by a daring German rescue party and became head of the Fascist puppet government set up in N Italy by Hitler.

On the German collapse (Apr., 1945) Mussolini was captured, tried in a summary court-martial, and shot with his mistress, Clara Petacci. Their bodies, brought to Milan, were hanged in a public square and buried in an unmarked grave. Mussolini's body was later removed, and in 1957 it was placed in his family's vault.