Martin was elected pope without seeking prior approval from the Byzantine emperor. He firmly condemned the heresy of the Monothelites—those who taught that Christ had only one will rather than two, human and divine, corresponding to his two natures as the Incarnate Word. This condemnation was made in defiance of Emperor Constans II, who then sent an officer named Olympius to arrest the pope. Once in the West, however, Olympius declared his independence and usurped power in Italy.
Eventually, the emperor succeeded in having Martin brought to Constantinople. Accused of complicity with Olympius, he was condemned to death, a sentence that was later commuted—at the request of Patriarch Paul II—to exile. Meanwhile, the Roman clergy elected a new pope, which caused Martin deep sorrow. Of fragile health, he did not survive more than a year in banishment.
He died in Cherson, in Crimea, on September 16, 655. Because of the popularity of his namesake, Saint Martin of Tours (commemorated on November 11), the pope’s memory was long celebrated on November 12 as that of a martyr. Today, however, following the witness of the Greek Life of Martin, which records his death on April 13, the Church keeps his feast on this date—shared also by the Byzantine liturgy.