Martin was born at Todi in Umbria and served the Roman Church as a papal apocrisarius (diplomatic legate) at the imperial court in Constantinople before his election to the see of Peter in 649.
His pontificate immediately confronted the Monothelite heresy — the Byzantine imperial theology that Christ had only one will (a compromise meant to placate the Monophysites of Egypt and Syria). Within three months Martin convened the Lateran Council of 649, which condemned both Monothelitism and the imperial edict (the Typos) that had forbidden discussion of it.
The Emperor Constans II had Martin arrested in 653 — too ill to resist, he was taken in chains by sea to Constantinople, paraded in public, denied medical care, and sentenced to death (later commuted) for treason. Exiled to Cherson in the Crimea — a desolate outpost at the edge of the empire — he died there of hunger and neglect in 655, having written touching letters of forgiveness for his enemies and pleas for food that survive.
He is the last pope to be venerated as a martyr by the universal Church. His feast on April 13 is one of the oldest martyr-feasts in the calendar.