A third son from a junior branch of his family, he sold his castle to equip himself as a knight, became a protégé of Guy II de la Roche, Duke of Athens, expelled the Byzantines from Euboea in 1296, and advanced to become one of the most powerful lords of Frankish Greece.

Boniface was also wed to a lady, identified as "Agnes de Cicon" by some 19th-century and 20th-century historians, whose dowry included titles to the island of Aegina and of Karystos on the southern tip of Euboea.

This campaign made him the most powerful person in Euboea: in addition to Karystos, which he claimed by right of his wife, he held on to the other forts he had captured, aided by the fact that most of the surviving claimants of the Lombard triarchies were women.

At the same time, however, the Republic of Venice increasingly made its presence felt on the island through its colony at the city of Negroponte (Chalkis), and through the rising influence of the local Venetian representative, the bailo.

[6][7] In 1302 or 1303, following the sudden death of the Greek ruler of Thessaly, Constantine Doukas, the region passed into the hands of his underage son, John II.

According to the Chronicle of the Morea, Boniface joined Guy and the Marshal of the Principality of Achaea, Nicholas III of Saint Omer, with a hundred knights.

Her proposal was accepted, and the Frankish army moved north into Byzantine-controlled lands around Thessalonica, until the Italian-born Empress Yolande of Montferrat, who held the city as her own domain, convinced them to withdraw without further incident.

Walter of Brienne now engaged them to fight against John II Doukas, who had turned against the Frankish tutelage and, seeking to make himself independent, joined forces with Epirus and the Byzantines.

The details of the battle are unclear, but the Frankish heavy cavalry charge was apparently impeded by the marshy terrain, allowing the Catalans and their Turkish auxiliaries to prevail.

Lacking a leader of sufficient social standing, at first they turned to Boniface, who was now the most important surviving Frankish noble in the whole of northern Greece, and whom they esteemed greatly; Muntaner described him as "the wisest and most courteous nobleman that was ever born".

Fearing reprisals from Venice in Negroponte, and loath to antagonize the rest of Frankish Greece, at a time when the permanence of the Catalan regime was still uncertain, Boniface declined the honour.

[1][19] In 1317, however, in a dispute between Boniface and the Venetian Andrea Cornaro, ruler of half a triarchy, the Catalans took the side of the latter and supplied 2,000 soldiers to bolster the garrison of Chalkis.