Pope Theodore I was a steadfast defender of faith who led the Catholic Church during a time of great theological and political turmoil. His unwavering opposition to the Monothelite heresy, left a lasting impact on the Church and the Roman Empire.

Pope Theodore I, of Greek descent, led the Catholic Church from AD 642 to AD 649 as the Seventy-Third Pontiff. Born in Jerusalem as the son of a bishop, he fled to Rome to escape the invasion by the Caliphate. In AD 640, Pope John IV made him a cardinal deacon. After John IV's death, Theodore was elected pope and quickly received approval from the Emperor’s representative in Ravenna.

During the reign of Pope Theodore I, the heresy of Monothelitism remained strong in the Eastern Church. He was chosen as pope partly because of his Eastern origins and firm opposition to this teaching, as the Church sought to resist imperial pressure to accept it.

One of his first actions was to write to Emperor Constans II, questioning why the Ecthesis—an official document supporting Monothelitism—was still in force, even though both Pope John IV and Emperor Heraclius had refused to withdraw it. He also wrote to the new Patriarch of Constantinople, Paul II, urging him to reject the Ecthesis and remove it from public display.

The exiled Patriarch Pyrrhus I of Constantinople, after losing a debate with Maximus the Confessor on Monothelitism and the Ecthesis, rejected the heresy. He then traveled to Rome, where he publicly confessed the true faith in St. Peter’s Basilica. Pope Theodore I welcomed him with honor and recognized him as the rightful Patriarch of Constantinople.

However, the current patriarch, Paul II, refused to reject the Ecthesis and was excommunicated by Pope Theodore. Later, Pyrrhus I changed his stance again, went to Ravenna, reconciled with the emperor, and renounced his confession of faith. In response, Pope Theodore convened a synod in Rome and excommunicated Pyrrhus I. According to tradition, the pope signed the decree at St. Peter’s tomb using Eucharistic wine.

By AD 642, the Ecthesis had failed to unite Monophysite supporters in the East with the Church. Realizing its unpopularity in the West could cause instability, Emperor Constans II issued the Typos, rescinding the Ecthesis and banning further debate on Christ’s nature and works. He decreed that Church teachings should follow the first five ecumenical councils. However, when the Apostolic Nuncio in Constantinople refused to sign the decree, the emperor had him arrested and exiled. The Latin Chapel in the Placidia Palace, the Nuncio’s residence, was then closed, and its altar destroyed.

Before responding to Emperor Constans II's Typos, Pope Theodore I passed away on 14 May AD 649.