He was born Mauritius Burchinus (Maurice Bourdin) in the Limousin, part of Aquitaine. He was educated at Cluny, at Limoges, and in Castile, where he was a deacon at Toledo. In 1098/1099 his Cluniac connections recommended him as Bishop of Coimbra. After a four year pilgrimage to the Holy Land, he was made Archbishop of Braga in 1111. There he was one of the principal agents of the Burgundian Henry, Count of Portugal, in his reorganization of the Portuguese church.
Portugal was then a fief of Castile, and the ambitious Count Henry pursued a vigorous program of ecclesiastical and political autonomy. By 1114, Mauritius had become embroiled in a dispute with the Spanish primate and papal legate in Castile, Bernard of Toledo, to the extent that he was called to Rome and suspended by Pope Paschal II. Nevertheless, he found favor at the papal court, and in 1116, when Henry V, Holy Roman Emperor invaded Italy during the ongoing confrontations over the Emperor's rights of investiture of clerics, Paschal II sent Mauritius on an embassy to him, while the Pope and the Curia fled south to Benevento. Mauritius defected to the Emperor's side. Henry went to Rome, and on Easter Sunday, March 23, 1117, was crowned Holy Roman Emperor by Mauritius. Paschal deposed and excommunicated Henry and removed Mauritius from office.
When Paschal died on 24 January 1118, he was succeeded by Gelasius II. Henry went to Rome but Gelasius escaped to Gaeta and refused to meet the Emperor to discuss German affairs. Partly in reprisal the imperial party among the cardinals then annulled Gelasius' election, and on March 1 Mauritius was proclaimed pope, taking the name Gregory VIII. Gelasius, at Capua, proceeded to excommunicate both Gregory and Henry (April 7).
After Gelasius' death, when Callixtus II had been elected Pope in 1119, Henry was induced to change papal allegiance, in the Concordat of Worms of 1122. Callixtus entered Rome, and Gregory left, going to Sutri, where he was in April 1121, when papal troops of Callixtus closed up the city for eight days until its citizens surrendered Antipope Gregory. He was taken to Rome and imprisoned in the Septizonium. After having been moved in confinement from monastery to monastery, he finally died at La Cava, Salerno, some time after August 1137.