The church has followed the spread of the Ukrainian diaspora and now has some 40 hierarchs in over a dozen countries on four continents, including three other metropolitan bishops in Poland, the United States, and Canada.
The head of the church is Major Archbishop Sviatoslav Shevchuk, since March 2011.
Within Ukraine itself, the UGCC is a minority of the religious population, being a distant second to the majority Eastern Orthodox faith.
The 9th-century mission of Saints Cyril and Methodius in Great Moravia had particular importance as their work allowed the spread of worship in the Old Church Slavonic language.
The Byzantine-Greek influence continued, particularly with the official adoption of Byzantine rites by Prince Vladimir I of Kiev in 988 when there was established the Ecumenical Patriarch of Constantinople Metropolis of Kiev and all Ruthenia.
Later at the time of the Great Schism (ca 1054) the Ruthenian (Rusyn) Church took sides and remained Orthodox.
In terms of number of members, the Ukrainian Greek Catholic Church ranks third in allegiance among the population of Ukraine after the Ukrainian Orthodox Church (Moscow Patriarchate) and the Ukrainian Orthodox Church - Kyiv Patriarchate.
Currently, the Ukrainian Greek Catholic Church predominates in three western oblasts of Ukraine, including about half the population of Lviv, but constitutes a small minority elsewhere in the country.
The Ruthenian Uniate Church was created with the Union of Brest in 1595/1596, yet its roots go back to the very beginning of Christianity in the Mediaeval Slavic state of Ruthenia.
Byzantine missionaries exercised decisive influence in the area.
It is the second-largest particular church (sui juris) in the Catholic Church (after the Latin, or Roman, Church).
It traces its origin to the Ruthenian Uniate Church (Latin: that existed before the partition of Poland.
The primate of the church holds the office of Archbishop-Major of Kyiv-Halych and All Ruthenia, though the hierarchs and faithful of the church have acclaimed their primate "Patriarch" and have requested Papal recognition of, and elevation to, this title.
The church is one of the successor churches to the acceptance of Christianity by Grand Prince Vladimir the Great of Kiev, in 988.