Baldwin was the nephew of Baldwin IV (Baldwin the Leper), king of Jerusalem, and his successor. His mother was princess Sybilla; his fatrher,. her first husband, WIlliam of Monferrat. He was born in 1177CE, and was crowned co-king with his uncle in 1183, before succeeding to the throne in his own right in 1185 on the death of Baldwin IV.
As regent he had Count Raymond of Tripoli, but he was little more than a pawn -- during his life, his uncle had continued to govern, even as he became blind and paralysed; on his death Baldwin V was still too young to take any decisions for hismelf.
And, within a year, in the summer of 1186, he was dead, leaving a complicated succession crisis which eventually saw Sybilla his mother taking the throne, on condition that she divorce her Lusignan husband, Guy.