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who made christianity the official religion of the roman empire

The Roman emperor Theodosius I is generally credited with making Christianity the official state religion of the Roman Empire, through the Edict of Thessalonica in 380 CE, issued together with co-emperors Gratian and Valentinian II.

Quick Scoop: Core Answer

  • In 380 CE, Emperor Theodosius I issued the Edict of Thessalonica, declaring Nicene Christianity the official religion of the Roman Empire.
  • The decree was formally issued in the names of Theodosius I (East), Gratian (West), and the young co-emperor Valentinian II.
  • This went beyond mere tolerance and effectively elevated Nicene Christianity above all other beliefs in the empire.

Before Theodosius: From Persecuted to Preferred

  • Earlier emperors often persecuted Christians, especially in the 3rd century, treating Christianity as an illegal or suspicious cult.
  • A major turning point came under Constantine with the Edict of Milan in 313 CE, which granted religious toleration to Christians and other faiths rather than making Christianity official.
  • Constantine supported the church financially, built churches, and favored Christians in imperial appointments, laying political and social groundwork for a Christian empire.

What Theodosius Actually Did

  • The Edict of Thessalonica (380 CE) ordered all subjects to follow the faith taught by the bishops of Rome and Alexandria, framing Nicene Christianity as the only legitimate form of Christianity.
  • The law described those who rejected this creed as heretics, depriving them of the name “Catholic Christians” and often limiting their rights and legal standing.
  • Theodosius’ broader legislation then increasingly restricted traditional pagan worship and non‑Nicene Christian groups, pushing the empire toward a religious monopoly in practice.

Was It Just One Emperor?

Historians usually distinguish between three stages:

  • Toleration : Constantine and Licinius (Edict of Milan, 313) ended persecutions and legalized Christianity but did not make it the official religion.
  • Imperial Favor : Fourth-century Christian emperors after Constantine gave privileges and support to the church, while still allowing other cults to exist.
  • State Religion : Theodosius I’s policies (Edict of Thessalonica in 380 and later anti-pagan and anti-heretical laws) effectively made Nicene Christianity the state religion.

So, while several emperors contributed to the process, Theodosius I is the one most directly associated with making Christianity the official religion of the Roman Empire.

Information gathered from public forums or data available on the internet and portrayed here.