MOSCOW — Ukraine took a major step on Saturday toward establishing its own, autonomous Orthodox Church, setting the stage for increased tensions with Russia by altering a centuries-old religious tradition under which the Kiev church answered to Moscow.

Some 190 bishops, priests and other church figures spent the day closeted in St. Sophia’s Cathedral in downtown Kiev to elect the newly unified Ukrainian church’s head, Metropolitan Epiphanius. He is scheduled to travel in January to Istanbul, the historical seat of the Eastern Orthodox Church, to receive an official order granting autonomy.

Hundreds of supporters of the move cheered and some wept as President Petro O. Poroshenko, who had attended the session, emerged from the cathedral to announce that Ukraine had a new church leader.

Quoting from the national poet, Taras Shevchenko, Mr. Poroshenko said that “Ukraine will no longer drink Moscow poison from the Moscow cup,” and he called on supporters to remember the day’s events as “the final acquisition of independence from Russia.”