Henry was the second emperor of the Latin Empire of Constantinople. He was a younger son of Baldwin V, Count of Hainaut (later Baldwin VIII, count of Flanders), and Margaret I of Flanders, sister of Philip of Alsace, count of Flanders.
Having joined the Fourth Crusade in about 1201, he distinguished himself at the sieges of Constantinople and elsewhere. During the July 1203 siege, Henry was one of eight division generals, the others including Boniface of Montferrat (the crusade leader), Doge Enrico Dandolo (leader of the Venetians), Louis of Blois (one of the first nobles to take the cross), and Henry's own brother, Baldwin of Flanders, who controlled the largest division. During the 1204 siege, Henry led a chevauchée expedition to gain supplies and raided a castle in Philia, near the Black Sea with, according to Robert de Clari, about 30 knights and an unspecified number of mounted sergeants. An ambush was laid for him by Emperor Alexius V "Murzuphlus" Ducas, but Henry and his force routed the Greeks soundly, captured a revered icon supposedly containing relics of Christ, and returned to the crusader camp. He soon became prominent among the princes of the new Latin Empire.
When his elder brother, the emperor Baldwin I, was captured at the Battle of Adrianople in April 1205 by the Bulgarians, Henry was chosen regent of the empire, succeeding to the throne when the news of Baldwin’s death arrived. He was crowned 20 August 1206.
The emperor died, poisoned, it is said, by Oberto II of Biandrate, ex-regent of Thessaloniki, on 11 June 1216, probably at the instigation of his wife, Maria of Bulgaria. On his death his brother-in-law Peter Courtenay was crowned emperor in Rome, but never arrived in Constantinople. In the years 1217 to 1219, therefore, the Latin Empire was effectively ruled by Yolanda, Henry's sister and Peter's wife, in regency. The last two Latin emperors were Peter and Yolanda's sons Robert and Baldwin.