The history of Christianity in Ukraine dates back to the earliest centuries of the history of Christianity, to the Apostolic Age, with mission trips along the Black Sea and a legend of Andrew the Apostle even ascending the hills of Kiev. The first Christian community on territory of modern Ukraine is documented as early as the 4th century with the establishment of the Metropolitanate of Gothia, which was centered in the Crimean peninsula. However, on territory of the Old Rus in Kiev, Christianity became the dominant religion since its official acceptance in 989 by Vladimir the Great (Volodymyr the Great), who brought it from Byzantine Crimea and installed it as the state religion of medieval Kievan Rus (Ruthenia), with the metropolitan see in Kiev.

Although separated into various Christian denominations, most Ukrainian Christians share a common faith based on Eastern Christianity. This tradition is represented in Ukraine by the Byzantine Rite, the Eastern Orthodox and Eastern Catholic churches, which have been at various historic times closely aligned with Ukrainian national self-identity and Byzantine culture.

Being officially eliminated since the end of World War II, the recent revival of Ukrainian national religions started just before dissolution of the Soviet Union in 1989 with reestablishment of the Ukrainian Greek Catholic Church which also triggered recovery of the Ukrainian Autocephalous Orthodox Church movement out of diaspora and transition of the former Russian Orthodox Church clergy who were native Ukrainians. Today, there are three national Ukrainian churches: the Orthodox Church of Ukraine, the Ukrainian Greek Catholic Church, and the Ukrainian Orthodox Church. Additionally, there is a smaller number of Byzantine rite adherents in the Ruthenian Greek Catholic Church who were dominated by the Kingdom of Hungary in the past. Western Christian bodies including the Latin Church of the Catholic Church and several Protestant denominations have had a limited presence on the territory of Ukraine since at least the 16th century and represent a minority of Christians in the country.

Andrew the apostle is believed to have travelled up the western shores of the Black Sea, to the area of present-day southern Ukraine, while preaching in the lands of Scythia. Legend (recorded in the Radziwiłł Chronicle) has it that he travelled further still, up the Dnieper River, until he came to the location of present-day Kiev in AD 55, where he erected a cross and prophesied the foundation of a great Christian city. Belief in the missionary visit of Andrew became widespread by the Middle Ages, and by 1621, a Kiev synod had declared him the "Rus'-apostle". Titus, a disciple of Andrew, is also venerated in Ukrainian churches, as are three "Scythian" disciples, Saints Ina, Pina and Rima, who accompanied him to Kiev. Both the 18th-century Church of St Andrew and an earlier structure from 1086 it replaced were purportedly built on the very location of the apostle's cross, planted on a hill overlooking the city of Kiev.

Although the Primary Chronicle refers to the apostle continuing his journey as far north as Novgorod, Andrew's visit to any of these lands has not been proven, and in fact may have been a later invention designed to boost the autocephalic aspirations in the territories where the upper clergy continued to be dominated by Greeks for several centuries.

These first half-legendary Christian churches on the territory of present Ukraine were eliminated by the Gothic invasion in the third century. The head of the "Scythian bishopric" presented at the First Ecumenical Council in Nicaea in 325 probably in fact was Bishop Cadmus from the Bosporan Kingdom.

Pope Clement I (ruled 88–98) was exiled to Chersonesos on the Crimean peninsula in 102, as was Pope Martin I in 655. Furthermore, it has been definitively recorded that a representative from the Black Sea area, the "head of the Scythian bishopric", was present at the First Council of Nicaea in 325, as well as the First Council of Constantinople in 381; it has been surmised that this representative would have to have been Bishop Cadmus of the Bosporan Kingdom. Ostrogoths, who remained on present-day Ukrainian lands after the invasion of the Huns, established a metropolinate under the Bishop of Constantinople at Dorus in northern Crimea around the year 400. A bishop's seat had also existed since 868 across the Strait of Kerch, in the ancient city of Tmutarakan. The Polans and the Antes cultures, located so close to the Crimea, surely became familiarized with Christianity by this time.

The relics of Pope Martin were allegedly retrieved by the "Equal-to-apostles" brothers Cyril and Methodius, who passed through present-day Ukraine on their way to preach to the Khazars. Sent from Constantinople at the request of the ruler of Great Moravia, these brothers would add to foundation of Christianity in Ukraine by creating the Glagolitic alphabet, a precursor to the eponymous "Cyrillic script", which enabled the local population to worship God in Old Church Slavonic, a language closer to the vernacular Old East Slavic language than the Greek used to worship in Constantinople, or Latin in the west.