His early life is little known. It is repeatedly claimed that he entered the Order of Benedictines but this is not proven. Pope Innocent III created him Cardinal-Deacon of S. Lucia in Septisolio around 1206. Later, he was promoted to the rank of Cardinal-Priest of S. Cecilia (probably on April 2, 1211), and finally opted for the suburbicarian see of Albano in the spring of 1213. He subscribed the papal bulls between May 4, 1207 and January 26, 1230. He was sent on a diplomatic mission to Constantinople in 1213. During this two-year mission he attempted to close Orthodox churches and imprison the clergy, but this caused such domestic upset that Henry of Flanders, the Latin Emperor, reversed his actions which had caused the "tempest which held the city of Constantine in its grip", as noted a contemporary historian. Three years later he was elected Latin Patriarch of Antioch but his election was not ratified by the Holy See. Dispatched by Pope Honorius III to lead the Fifth Crusade at Damietta in Egypt, he made a poor strategic decision in turning down peace offers made by Al-Kamil. He became dean of the Sacred College of Cardinals at the election to the papacy of Cardinal Ugolino Conti (Pope Gregory IX) on March 19, 1227. He was one of the leader of the papal army in 1229/30 during the struggle with the Emperor Frederick II. He died at Montecassino and was buried there.
- Akropolites, George (Ruth Macrides, ed). The History. Oxford: University Press, 2007.
- Joseph P. Donovan (1950), Pelagius and the Fifth Crusade
- Werner Maleczek (1984), Papst und Kardinalskolleg von 1191 bis 1216, Vienna
- Biographical entry by Salvador Miranda
- Araldica Vaticana
- Peter Linehan: The Spanish Church and the Papacy in the 13th Century, Ch. 12 (Spaniards at the Curia)
- Galvani is a Latin form; he is listed also as Pelágio Galvão, Pelayo Gaytan, Pelagio di Santa Lucia, Pelagius of Albano, Pelagius of St. Lucia, Pelagius Albanensis. According to Maleczek, p. 166 note 320, this commonly accepted family name of Pelagio remains uncertain because is based only on the fact, that one of his nephew was called with this familiar denomination; Maleczek observes that it is possible that this relationship was on the maternal side.
- In older historiography (e.g. Pius B. Gams, Series episcoporum Ecclesiae catholicae, p. XXII) death of Cardinal Pelagio is postdated by 10 years (to 1240). The correct date is given by Peter Linehan: The Spanish Church and the Papacy in the 13th Century, Ch. 12 (Spaniards at the Curia), Donovan, p. 115, and Maleczek, p. 169. The latest source adds that on July 23, 1230 the Cardinal is referred to as of bone memorie.
- Some sources indicate that he was Portuguese, but Antonio García y García, ‘La canonística ibérica (1150–1250)en la investigación reciente’, Bulletin of Medieval Canon Law, 11 (1981), 41–75, at pp. 54–55; and Maleczek, p. 166, have proven that several contemporary documents attest his Leonese origins. Perhaps he was Galician.
- According to Maleczek,p. 166, the theory that he was Benedictine is based only on the fact that he died at Montecassino, and, therefore, his death has been recorded in the necrology of the abbey.
- S. Miranda places his promotion in 1205. Maleczek, p. 290 and 385, says that he was possibly created in the great consistory celebrated on May 27, 1206 but that the first documentary certification of his cardinalate is dated May 4, 1207. In any case, he was created no later than in the spring of 1207.
- Maleczek, p. 290
- Maleczek, p. 167
- George Akropolites, p. 155.
- He was Cardinal-Bishop next to Ugolino Conti in the order of seniority.
- Maleczek, p. 169