Initially offered the Kingdom of Jerusalem, Eustace was at Apulia when he received news of Baldwin of Bourcq's election to the throne.
[2] While waiting for Robert Curthose's arrival from Normandy, Eustace and his fellow compatriots were besieged at Rochester castle by William II.
[5] In 1091, Eustace was with Robert Curthose when the latter agreed to terms with William II, recognizing him as king of England.
[9] Eustace, as a member of the council held at Ruj on 4 January 1099, mediated the conflict over the control of Antioch between Bohemund of Taranto and Raymond IV of Toulouse.
Eustace commanded a division of the crusader army during the Battle of Ascalon,[12] and was a patron of the Knights Templar.
To commemorate Eustace's crusading adventures, the mint at Boulogne struck silver coins with a lion above the walls of Jerusalem stamped on the obverse.