He was a member of the noble Barbo family and a third cousin of Pietro Barbo, who became Pope Paul II. In Rome he resided in the Palazzo di San Marco, as did the Venetian pope, who elected not to remove to the Vatican. From 1467 he was the cardinal patron of the Knights of Rhodes, for whom he built the loggia on the imperial forums. At Paul's death, he was absent from Rome for several years; on his return he commissioned Paul's tomb from Mino da Fiesole, who completed it in 1477 for Old St. Peter's Basilica; fragments are conserved in the Vatican Museums. Barbo participated in the Papal conclave, 1471, which elected Pope Sixtus IV, for whom he served as legate to Germany, Hungary and Poland, with the charge, in which he was unsuccessful, of promoting a crusade against the Turks. He left Rome 22 February 1472 and went to the court of Frederick III, Holy Roman Emperor, whom he was unable to inspire to combat the Ottoman Turks. Barbo returned to Rome 26 October 1474. Possessed of several abbacies in commendam, he was elected Camerlengo of the Sacred College of Cardinals and bishop of Palestrina, where he restored the cathedral. His diplomacy defused the partisan tensions that were building in Rome before the conclave of 1484. For a price, he secured the Castel Sant'Angelo from Girolamo Riario and convinced both Orsini and Colonna factions to evacuate the city, leaving the conclave in security and peace. During the consistory, Barbo was one of those considered papabile; the election of Pope Innocent VIII was a compromise effected between cardinals Della Rovere and Rodrigo Borgia to block the candidacy of the Cardinal of St. Mark. Barbo was the eldest son of Marino Barbo and Filippa della Riva. He was an erudite patron of the humanists so distrusted by Paul II, but as chancellor of the Sapienza, he was constrained to withhold the salary of Pomponio Leto, who had fled to Venice. Marco Barbo assembled an outstanding library; generous and charitable, he distributed all his wealth to the poor of Rome at his death.
