Baldwin of Bourcq was the cousin of Godfrey of Bouillon and Baldwin of Boulogne. He was one of the major knights who set out on the First Crusade.

Baldwin of Boulogne, the first Count of Edessa, appointed Baldwin of Bourcq count when the former became king of Jerusalem in 1100. Baldwin was captured by Seljuk Turks in 1104 after the Battle of Harran, but was ransomed in 1108. Upon the death of his cousin in 1118, he became king of Jerusalem as Baldwin II. Almost immediately, the kingdom was simultaneously invaded by the Seljuks from Syria and the Fatimids from Egypt, although by showing himself ready and willing to defend his territory, Baldwin forced the Muslim army to back down.

In 1119, the Crusader Principality of Antioch was invaded, and the Crusaders were defeated in a battle they came to call Ager Sanguinis (the Field of Blood). Although it was a crushing blow, Baldwin helped Antioch recover and drive out the Seljuks later that year.

Baldwin was captured by the Seljuks while patrolling the borders of his former county of Edessa in 1123, and was held captive until he was ransomed in 1124. Meanwhile, the Crusaders besieged and captured Tyre, with help from a Venetian fleet. This would lead to the establishment of Venetian and other Italian trading colonies in the coastal cities of the kingdom, which were autonomous and free from taxes and military duties.

Also during the reign of Baldwin II, the first two military orders were created. In 1118, Hughes de Payens founded the Knights Templar in Jerusalem, while the Knights Hospitaller, which had been founded in 1113, turned into a military order as opposed to the charitable order they had originally been.

In 1125 Baldwin assembled the knights from all the Crusader territories and met the Seljuks at the Battle of Azaz. Although the Seljuk army was much larger, the Crusaders were victorious, and they restored much of the influence they had lost after the Ager Sanguinis. Had Antioch and Edessa not been fighting amongst themselves after the battle, Baldwin may have been able to attack Aleppo; however, Aleppo and Mosul were soon united under Zengi in 1128. Unable to attack either of those cities, Baldwin attempted to take Damascus in 1128 with the help of the Templars, but the attempt failed.

He married in 1101 to Morphia of Melitene, the daughter of the Armenian prince Gabriel of Melitene. Baldwin had no sons, but had four daughters, Melisende, Alice, Hodierna, and Joveta. He arranged for Melisende to marry Fulk of Anjou in 1129; Fulk and Melisende ruled jointly when Baldwin died in 1131. Alice married Bohemund II of Antioch and Hodierna married Raymond II of Tripoli.