Itagaki Taisuke was born into a middle-ranking samurai family in Tosa Domain, (present day Kōchi Prefecture), After studies in Kōchi and in Edo, he was appointed as sobayonin (councillor) to Tosa daimyō Yamauchi Toyoshige, and was in charge of accounts and military matters at the domain's Edo residence in 1861.

During the Boshin War, he emerged as the principal political figure from Tosa domain as a leader of the Jinshotai assault force, and claimed a place in the new Meiji government after the Tokugawa defeat.

In 1874, together with Gotō Shōjirō of Tosa and Etō Shinpei and Soejima Taneomi of Hizen, he formed the Aikoku Kōtō (Public Party of Patriots), declaring, "We, the thirty millions of people in Japan are all equally endowed with certain definite rights, among which are those of enjoying and defending life and liberty, acquiring and possessing property, and obtaining a livelihood and pursuing happiness.

Itagaki's involvement in liberalism lent it political legitimacy in Japan, and he became a leader of the push for democratic reform.

[1] Itagaki and his associations created a variety of organizations to fuse samurai ethos with western liberalism and to agitate for a national assembly, written constitution and limits to arbitrary exercise of power by the government.

After funding issues led to initial stagnation, the Aikokusha was revived in 1878 and agitated with increasing success as part of the Freedom and People's Rights Movement.

[2] They enticed Itagaki to return as a sangi (councilor): however, he resigned after a couple of months to oppose what he viewed as excessive concentration of power in the Genrōin.

[citation needed] Itagaki criticized the government at the same time as it was under threat by the 1877 Satsuma Rebellion, which turned the cabinet against him.

[3] In response, Itagaki created the Liberal Party (Jiyuto) together with Numa Morikazu in 1881, which, along with the Rikken Kaishintō, led the nationwide popular discontent of 1880–1884.

The trip turned out to have been provided by the Mitsui Company, but suspicions that Itagaki was being won over to the government side persisted.