Methodius was the elder brother, born at Thessalonica around 815, and his early career was administrative rather than scholarly. He governed a Slav-populated district before withdrawing to a monastery on Mount Olympus in Bithynia. He joined his brother for the Khazar embassy and then for Moravia in 863, and after Constantine's death at Rome in 869 the whole undertaking was his to carry alone.
The papacy backed it. He was consecrated archbishop with jurisdiction over Pannonia and Moravia, which revived an ancient see and also cut straight across territory the Bavarian bishops considered theirs. Their answer was direct. Around 870 he was seized, tried before a synod of Frankish bishops, and held in confinement in Bavaria for roughly three years, until Pope John VIII intervened, secured his release and instructed that the Slavonic liturgy be permitted.
He went back and kept working. The tradition credits him with translating most of the remaining books of the Bible into Slavonic in his last years, together with a collection of canon law for the new church. He died on 6 April 885, having named a successor. The Frankish party did not accept the succession, and within a short time his disciples were driven out of Moravia altogether.