Following the Moldo-Wallachian union of 1859, and the 1881 creation of the Kingdom of Romania, the seat in Bucharest became an archdiocese (April 7, 1883) and the one in Iaşi a diocese, replacing the Franciscan-led diocese of Bacău (June 27, 1884).
Romania accommodated various Catholic organizations, including the Institute of the Brothers of the Christian Schools (who operated three Bucharest schools by 1913), the Sisters of Mercy, the Passionists, and the Congregation of Notre-Dame de Sion.
The oldest traces of Roman Catholic activities on present-day Romanian territory were recorded in Transylvania, in connection to the extension of Magyar rule and the region's integration into the Kingdom of Hungary (see History of Transylvania).
Coinciding with the Habsburg offensives, religious conflicts were resumed and, in 1601 Bishop Demeter Napragy was forced out of Alba Iulia, with the see being confiscated by Protestants (although bishops continued to be appointed, they resided abroad).
Around that time, the ethnic Romanian Transylvanian intellectual Gheorghe Buitul joined the Jesuit order, the first member of his community to study in the Roman College of Rome, while the Transylvanian-born István Pongrácz was one of the Jesuits executed by Calvinists in Royal Hungary (1619).
It is the second largest Romanian denomination after the Romanian Orthodox Church, and one of the 16 state-recognized religions.
Overall data for 2011 indicated that there were 870,774 Romanian citizens adhering to the Roman Catholic Church (4.3% of the population). The Romanian Church United with Rome, Greek-Catholic is a related sui iuris Catholic Church which uses the Byzantine Rite.
In 1657, Armenians in Transylvania who belonged to the Armenian Apostolic Church and were led by Bishop Oxendius Vărzărescu, placed themselves under indirect Roman Catholic jurisdiction, as part of the Armenian Catholic Church.
It was also under Maria Theresia that Catholic teaching and school administration came under the supervision of the Commissio catholica (this remained the rule under the Austrian Empire and the early years of Austria-Hungary).
Four other dioceses function in Romania and are based, respectively, in Timişoara (the Roman Catholic Diocese of Timişoara, representing the Banat), Oradea (the Roman Catholic Diocese of Oradea, for Crişana), Satu Mare (the Roman Catholic Diocese of Satu Mare, for Maramureş), and Iaşi (the Roman Catholic Diocese of Iaşi, for Moldavia).
The Church presently runs a faculty of theology (as part of the Babeş-Bolyai University in Cluj-Napoca), four theological institutes, six medical schools and sixteen seminaries (see Religious education in Romania).
The Diocese of Cumania disappeared for a while, as locals took over its property, but was revived in 1332-1334, when Pope John XXII appointed the Franciscan Vitus de Monteferro, the chaplain of King Charles Robert, as the new bishop.