Hugh's parentage is unknown, but William of Tyre called him "Hugo de Sancto Aldemaro", suggesting that he was descended from the powerful family of the hereditary castellans of Saint-Omer.

[4] Though no primary sources recorded in whose retinue he reached the Holy Land,[4] it is thought that he accompanied either Baldwin of Boulogne[5] or Robert II of Flanders.

[6] Baldwin and his elder brother, Godfrey of Bouillon, Duke of Lower Lorraine, departed for the crusade on 15 August 1096, and Robert II of Flanders about a month later.

[6] Hugh and Robert, Bishop of Lydda and Ramla took control of the Tower of David, enabling Baldwin to enter Jerusalem[6] on 9 November.

[12] Tancred accepted the offer and renounced Galilee in March 1101, but he also stipulated that the king should grant the same land "as a fief" to him if he returned to the kingdom within fifteen months.

[16] Thinking that the battle was lost, Hugh fled from the battlefield and hurried to Jaffa to inform the queen, traditionally called Arda, about the catastrophe.

[18] Hugh and his 80 knights hurried from Galilee to assist the royal army, but by the time they reached Arsuf on 19 May, the Egyptians had defeated the crusaders at Ramla.

[20] The arrival of hundreds of English, French, and Italian pilgrims enabled Baldwin to make a counter-attack, forcing the Egyptians to lift the siege on 27 May.