His older brothers Baldwin I (r. 1204–1205) and Henry (r. 1205–16) participated in the Fourth Crusade and were the first two emperors of the Latin Empire of Constantinople.
[1] In 1208 he was sent to command a garrison in the Rhodope Mountains, belonging to the autonomous prince Alexius Slav.
[2] In summer 1209, Henry quelled a revolt of the Lombard barons of the Kingdom of Thessalonica, and brought the realm under his effective control by appointing Eustace (along with Berthold of Katzenelnbogen) as his de facto viceroy there.
As confirmation of the pact, Eustace married a daughter of Michael and received a third of his lands as her dowry.
[3][4] Eustace is last mentioned in April 1217 as attending the coronation of the new Latin Emperor, Peter of Courtenay, and his sister, Yolanda of Flanders.