Office and Setting
Theodoritus served as a presbyter and keeper of the sacred vessels of the cathedral church in Antioch. The sources relate that this church had been built and adorned by the emperors Constantine the Great and his son Constantius, and that it was known on account of its splendor as the "Golden Church." As custodian of the sacred vessels, Theodoritus was responsible for the liturgical treasures of the cathedral.
Wikipedia describes him as a Greek-speaking Syrian Christian priest of Antioch, consistent with the city's place as a major center of Eastern Christianity in the fourth century.
Persecution under Julian the Apostate
After the death of the emperor Constantius, Julian the Apostate sought to restore paganism throughout the Roman Empire. According to the accounts, Julian appointed a relative of the same name, his uncle Julian, as governor in the East and at Antioch. This older Julian, himself an apostate from Christianity, was charged with closing the Christian churches and sending the valuables within them to the imperial treasury.
The synaxarion relates that the governor, together with an official named Felix, came to Antioch, placed Theodoritus under guard, and began to plunder the cathedral, profaning the altar and the holy table. A man named Euzoios who protested the sacrilege was killed. Theodoritus was falsely charged with concealing the church's valuables; he denied the charge and openly denounced Julian's apostasy and return to paganism.
Martyrdom
When Theodoritus rebuked the governor for his abandonment of the faith, he was subjected to severe torture, which the accounts say he endured with courage. By tradition he foretold that divine judgment would swiftly fall upon both the governor Julian and the emperor Julian. He was then beheaded. The synaxarion further relates that the soldiers who had tortured him were converted to Christ and afterward drowned.
The OrthodoxWiki and Wikipedia entries record the date of his death as October 22, 362, and report that the prophesied judgment was seen as fulfilled when the governor died of illness and the emperor Julian was killed during his Persian campaign. The cathedral commemoration recorded in the saint's own record is kept on March 8, with March 3 also given.
Relics
Wikipedia reports that his relics were later transferred to Uzes in southern France and enshrined in a cathedral there. This relic-translation is reported only by that source and is not corroborated by the synaxarion entries; the article itself notes that it relies heavily on primary sources.