The dates of his birth and death are unknown, as indeed are the details of his life outside the period spent in Jerusalem.
This allowed Manasses to establish himself in the east not only with the favour of his royal relatives but also with much land and money.
He assumed an insolent attitude of superiority towards the elders of the realm and refused to show them proper respect."
With his newfound power, he made many enemies among the more established older nobles, and Melisende's son Baldwin III especially hated him for keeping him out of government and alienating him from his mother.
He forced Manasses to surrender his castle of Mirabel, and captured Jerusalem from Melisende.