Born to an upper-rank Tosa samurai family, he served as a commander of imperial forces in the Boshin War of 1868. After the Meiji Restoration he became a state councilor but resigned in 1873 over the Korea debate alongside Saigo Takamori and Goto Shojiro. The following year, together with Soejima Taneomi, Goto, and Eto Shimpei, he submitted a memorial to the government calling for the establishment of an elected assembly and the expansion of civil rights—a pioneering act of the Freedom and People's Rights Movement. He founded the Risshisha in Kochi and organized the nationwide Liberal Party (1881), leading the civil rights movement. On April 6, 1882, when he was stabbed by an assailant at a speech venue in Gifu, he reportedly cried, 'Itagaki may die, but liberty never dies!'—words that live on as a symbol of the movement. Though the Liberal Party was later dissolved, Itagaki continued his civil rights activities. In his later years he was made a count and died on July 16, 1919, at eighty-three.

A man of passion and conviction. He combined samurai courage with genuine passion for civil rights ideology, and not even an assassin's blade could bend his beliefs. His stance of standing close to the common people won him wide support.

As the leader of the Freedom and People's Rights Movement he played an indispensable role in the development of Japanese parliamentary politics and democracy. 'Itagaki may die, but liberty never dies!' lives on forever as a famous saying symbolizing the spirit of Japanese liberalism.