He served as a papal legate on four occasions: to Poland and Hungary around 1124, to Carinthia in 1126, to the Crusader states in 1128 or 1129 and to Aquitaine from 1131 until 1137.
He took the side of the Antipope Anacletus II in the papal schism of 1130 and was deposed as cardinal-bishop by the Second Lateran Council in 1139.
An accomplished Latin stylist, Gilo wrote the majority of the Historia de via Hierosolymitana, a verse history of the First Crusade (1096–1099).
He also wrote the Vita sancti Hugonis abbatis Cluniacensis, a biography of Abbot Hugh of Cluny (1024–1109).
A couple of letters he wrote in connection with his third legation have also survived and are highly regarded for their style and eloquence.
In the explicit of two manuscripts, Gilo is said to have been a cleric of the diocese of Paris at the time he wrote the Historia, which was before he became a monk.
According to some sources, his is the third signature on the papal bull Ad universos fideles dated 28 December 1121, where his name appears as Aegidius Tusculanus episcopus.
At the request of Duke Bolesław III, Gilo confirmed the possessions of the Benedictine monastery of Tyniec acquired in 1105 and the boundaries of the new diocese of Włocławek.
[3] The purpose of Gilo's third legation was to resolve the dispute over the status of the archdiocese of Tyre, whether it was a suffragan of the patriarchate of Antioch or Jerusalem.
In 1127, Honorius II ruled in favour of Jerusalem, but Patriarch Bernard of Antioch refused to recognise the decision.
Honorius granted it and restated his ruling of the previous year, sending Gilo, an experienced legate, to enforce it.
He embarked for the Holy Land in the first half of July 1128 in Bari, taking the same ship as the archbishop of Tyre.
[3] Archbishop William II of Tyre mentions it in his Historia, while praising Gilo as a "most eloquent and literate man"[3] and his letters as "very famous".
Some sources have Gilo returning to Rome in December 1128 and signing papal privileges in March and April 1129,[2] while others have him in the Holy Land in 1129–1130.
Abbot Peter the Venerable wrote a letter dated no later than 1134 encouraging Gilo to change sides.
Although Gilo remained in France for several years, Gerard took the leading role in converting the French aristocracy to their faction.
[3] Gilo, joined by cardinals Gregory of Santa Maria in Aquiro and Roman of Sant'Adriano al Foro, was present in Bordeaux to witness this.
Also that year in Poitiers, acting in his capacity as papal legate, he resolved a dispute between the abbey of Montierneuf and its dependency of Foye-Montjault.
[2] Gerard died in March 1136 and that year Duke William X of Aquitaine abandoned the cause of Anacletus, making Gilo's position in Poitiers difficult.