The Transylvanian and Hungarian Unitarians represent the only branch of Unitarianism not to have adopted a congregationalist polity, and remains quasi-episcopal; the Northern Irish Non-subscribing Presbyterian Church, a distinct body closely related to Unitarianism, has a presbyterian structure. The Unitarian Church of Transylvania is administrated by a Bishop and two Curators-General, being dived into five Archpriestships. Since 1996, its Bishop is Árpád Szabó. The Church also endorses and teaches a catechism.
Together with the Calvinist Reformed Church and the two Romanian Lutheran churches (the Evangelical Lutheran Church and the Evangelical Church of Augustan Confession), the Unitarian community runs the Protestant Theological Institute of Cluj, wherein Unitarianism is represented by a distinct section. In addition, it has two high school-level theological educational institutions.
The vast majority of church adherents live in Transylvania, mostly between Sighişoara (Segesvár) and Odorheiu Secuiesc (Székelyudvarhely), more or less around Dârjiu (Székelyderzs). The Unitarian church is especially strong in Dârjiu, Atid (Etéd), Cristuru Secuiesc (Székelykeresztúr), Feliceni (Felsőboldogfalva), Inlăceni (Énlaka), and Mugeni (Bögöz), where Unitarians make up a large majority of the population.
The Unitarian Church was first recognized by the Edict of Torda, issued by the Transylvanian Diet under Prince John II Sigismund Zápolya (January 1568), and was first led by Ferenc Dávid (a former Calvinist bishop, who had begun preaching the new doctrine in 1566). Early on, the Unitarian Church had notable successes: it included 425 parishes, made use of the monumental St. Michael's Church in Cluj-Napoca, and attracted members of the eastern Transylvanian Székely community in large numbers.
The Church attracted suspicion from all other established religions, Roman Catholic as well as Protestant, with both camps deeming it heretic. After Dávid's imprisonment and 1579 death in custody, the institution entered a period of decline. Following the Union of Transylvania with Romania at the end of World War I, Unitarian congregations were established in regions of the Old Kingdom: the first Unitarian church in Bucharest was founded in 1933 (its building was later demolished).
Transylvanian Unitarian leaders have traditionally contributed to the activities of the England-based International Association for Religious Freedom (IARF), ever since the body was created in 1900. With the exception of 1920, it was present at all IARF congresses, and, in May 1975, Communist authorities allowed it to welcome the IARF's Executive Committee in the city of Cluj-Napoca. In 1994, the IARF European Conference was held in the same location. The Transylvanian Unitarian Church is also a founding member of the International Council of Unitarians and Universalists.
The locality of Dârjiu is home to a 13th century fortified Unitarian Church, which is on UNESCO's World Heritage List. Murals, dating back to the Roman Catholic period, show King Ladislaus I of Hungary's legend: Cumans broke into the Kingdom of Hungary; Duke Ladislaus, along with his cousin King Solomon, rode against them and freed a girl believed to be daughter of a Hungarian nobleman from a Cuman's hands (although she did not support this act). Further murals in the region are to be found at Unitarian churches in Mugeni, Crăciunel, and smaller ones in Rugăneşti and Cristuru Secuiesc.