He was a younger son of Yolanda of Flanders, sister of the first two emperors, Baldwin I and Henry of Flanders. Her husband, Peter of Courtenay, was third emperor of the Latin Empire (also known as Romania, not to be confused with modern Romania), and had been followed by his son Robert of Courtenay, on whose death in 1228 the succession passed to Baldwin, then an 11-year-old boy. The barons chose John of Brienne (titular king of the Kingdom of Jerusalem) as emperor-regent for life; Baldwin was to rule the Asiatic possessions of the empire when he reached the age of twenty, was to marry Johnís daughter Mary, and on Johnís death to enjoy the full imperial sovereignty. The marriage contract was carried out in 1234. Since the death of Baldwin's uncle emperor Henry of Flanders in 1216, the Latin Empire had declined and the Byzantine power advanced; and the hopes that John of Brienne might restore it were disappointed. He died in 1237.
The realm which Baldwin governed was little more than the city of Constantinople. His financial situation was desperate, and his life was chiefly occupied in begging at European courts. He went to the West in 1236, visited Rome, France and Flanders, trying to raise money and men to recover the lost territory of his realm. His efforts met with success, and in 1240 he returned to Constantinople (through Germany and Hungary) at the head of a considerable army. Circumstances hindered him from accomplishing anything with this help, and in 1245 he traveled again to the West, first to Italy and then to France, where he spent two years. The empress Maria and Philip of Toucy governed during his absence. He was happy to be able to get money from King Louis IX in exchange for relics. In 1249 he was with King Louis at Damietta.
The extremity of his financial straits reduced him soon afterwards to handing over his only son, Philip to merchants as a pledge for loans of money. Philip was later redeemed by Alfonso X of Castile. The rest of his reign was spent by Baldwin in mendicant tours in western Europe. In 1261 Constantinople was captured by Michael VIII Palaeologus, and Baldwinís rule came to an end. He escaped in a Venetian galley to Negropont, and then proceeded to Athens, thence to Apulia, finally to France. As titular emperor, his role was still the same, to beg help from the western powers. In 1267 he went to Italy; his hopes were centred in Charles of Anjou. Charles seriously entertained the idea of conquering Constantinople, though various complications hindered him from realizing it. He made a definite treaty with Baldwin to this intent (May 1267). During the next year Baldwin and his son Philip lived on pensions from Charles. In October 1273 Philip married Beatrice, daughter of Charles, at Foggia. A few days later Baldwin died.
Robert L. Wolff, "Mortgage and Redemption of an Emperor's Son: Castile and the Latin Empire of Constantinople," Speculum 29 (1954)
John of Brienne
Michael VIII Palaeologus
(restored Byzantine Empire)