Methodius was the eldest of the brothers, the administrator. He served first as governor of a Byzantine Slavic province on the Strymon river. Around 855 he abandoned the secular career and became a monk on Mount Olympus in Bithynia.
From 862 he was Cyril's older partner in the Moravian mission, traveling with him through Moravia and Pannonia, training Slavic-speaking clergy, supervising translations, and after Cyril's death in 869 continuing the mission alone for sixteen more years.
Pope Hadrian II named him archbishop of the new Pannonian see at Sirmium — restored after centuries of vacancy explicitly to provide a Slavic ecclesiastical authority independent of Frankish jurisdiction. Frankish bishops imprisoned him for nearly three years (870–873) until Pope John VIII intervened. He continued through the 870s and early 880s translating the rest of the Old Testament and the Church Fathers into Slavonic.
He died at Velehrad in Moravia on April 6, 885. His Slavic disciples — Sts. Clement, Naum, Gorazd, Sava, and Angelar — driven from Moravia after his death, took the Slavonic books to Bulgaria, where Prince Boris I established the Slavonic liturgy permanently. Through them the work of Cyril and Methodius produced the Cyrillic alphabet (named for Cyril, although developed later by Clement of Ohrid) and the entire literary tradition of Slavic Christianity — Bulgarian, Russian, Serbian, Macedonian, Ukrainian.