He was the son of Walter I of Brienne, count of Brienne, and his wife Eustachie of Tonnerre (Eustachie de Tonnerre [fr]).
[1] When Érard inherited the county of Brienne, he was invested by Theobald III, Count of Blois.
[2] Érard co-founded an abbey at Boulancourt, and later founded a monastery at Beaulieu.
[3] In 1114, Érard followed his liege lord, Hugh, Count of Champagne, to the Holy Land.
[4][5] In 1110 he married Alix of Roucy-Ramerupt,[1] daughter of André de Montdidier-Roucy, seigneur de Ramerupt and son of Hilduin IV, Count of Montdidier.