Pope Marinus II (; or Martin III; d. May 946) was Pope from 30 October 942 to his death in 946.
Marinus was born in Rome, and prior to becoming pope he was attached to the Church of Saint Cyriacus in the Baths of Diocletian. He was said to have encountered St. Ulrich on his visit to Rome in 909, and reportedly predicted Ulrich's eventual appointment as Bishop of Augsburg.
Marinus was elevated to the papacy on 30 October 942 through intervention of Alberic II of Spoleto, Prince of the Romans. He concentrated on administrative aspects of the papacy, and sought to reform both the secular and regular clergy. He extended the appointment of Frederick, Archbishop of Mainz as Papal Vicar and Missus dominicus throughout Germany and Francia. Marinus later intervened when the Bishop of Capua seized without authorization a church which had been given to the local Benedictine monks. In fact, throughout his pontificate, Marinus favoured various monasteries, issuing a number of Papal bulls in their favour.
Because of the similarity of the names Marinus and Martinus, Popes Marinus I and Marinus II were, in some sources, mistakenly given the name Martinus (and were then listed respectively as Martinus II and Martinus III). Thus, when the new Pope in 1281 took the name Martin, he became Pope Martin IV, when in fact he should've taken the name Martin II.