His brother was Hugh III of Gournay-en-Bray, and his cousins included Peter, Count of Dammartin and Hugh-Rainard, the bishop of Langres.
Pope Gregory VII entrusted Manasses with several delicate missions, but the bishop's character was not held in esteem by his former colleagues, the lower clergy.
According to Guibert of Nogent, writing in his memoirs thirty-five years later in 1115, Manasses was reported to have said that "the archbishop of Reims would be a fine thing, if one were not obligated to sing the Mass!"
Gregory VII intervened in 1077 to order Geoffrey, Bishop of Paris, to receive and absolve the monks fleeing into his territory.
In Autun on 10 September 1077, papal legate Hugh of Die condemned Manasses as a heresiarch, apparently for consenting to the elevation of the bishop of Senlis, suffragan of Reims, to his office by King Philip I. Manasses reacted by defending his conduct in a letter to Gregory and accusing the legates of acting in bad faith.