 In the 1840s, he became close to the poet Taras Shevchenko, and the historian Mykola Kostomarov and participated in the illegal Brotherhood of Saints Cyril and Methodius which envisioned a Ukrainian national rebirth, including national independence, within a free and equal Slavic federation.In 1847, Kulish was arrested for his participation in this organization, and spent some time in prison and a few years in exile.In the late 1850s, he was reunited with Kostomarov and others of the Cyril-Methodian "Brethren" and participated in the Ukrainian journal "Osnova" (The Foundation).