On 15 August 1214 Philippa married as her husband Erard I of Ramerupt, a powerful noble from Champagne, France. The couple married clandestinely in defiance of Pope Innocent III's prohibition of their marriage, due to the couple having been related within the prohibited degree of kinship. Pope Innocent was prompted by the machinations of her aunt Blanche of Navarre, who had also seized Erard's fiefs. Shortly after their marriage, Erard encouraged Philippa to claim her father's county of Champagne which had succeeded to her cousin Theobald IV, who was still a minor. His mother Blanche of Navarre acted as his regent and she violently defended her son's rights which soon led to open warfare.. In early 1216, Erard and Philippa returned to France, where they took up a position at Nevers, but were besieged by the forces of Blanche of Navarre. Most of the Champagne barons rallied around Erard and Philippa, however, the French king, Philippe II, Emperor Frederick II, and the Duke of Burgundy intervened on behalf of Blanche and her son. Supporters of Blanche also convinced a papal legate that the divorce between Queen Isabella and her first husband, Humphrey IV of Toron had been invalid, thus making Philippa and her sister Alice illegitimate. However, the validity of the divorce was upheld, as there had been no impediment to Maria of Montferrat's accession to the throne in 1205. The war finally ended upon Theobald reaching his majority in 1222, and in April of that year, Philippa was persuaded to renounce her claim to Champagne on behalf of her cousin. Theobald was however, obliged to pay Erard, Philippa and Alice a large monetary compensation. In addition to the generous financial settlement, Erard and Philippa were exempted from all payment of outstanding debts, and excommunication. After this time, Philippa and Alice abandoned their claim on Champagne. Together Erard and Philippa had:
Henri of Venizy, Seigneur of Ramerupt and Vénisy, married Marguerite de Salins by whom he had two sons.
Erard II of Ramerupt, married Mathilde by whom he had one daughter.
Marie de Brienne, married firstly Gaucher, Sire de Nanteuil-la Fosse, by whom she had three children; she married secondly Hughes II, Sire de Conflans, by whom she had one son.
Marguerite de Brienne, married Dirk Van Beveren, Burggraf of Dixmuiden, by whom she had issue. She became a nun after her husband's death.
Heloise de Brienne
Isabeau de Brienne, married firstly Henri V, Count of Grandpré, by whom she had three children; she married secondly Jean de Picquigny, by whom she had one daughter. Isabeau was the ancestress of Louis I, Count of Flanders.
Jeanne de Brienne, Dame de Séans-en-Othe, married before 1250 Mathieu III, Sire de Montmorency, by whom she had five children.
Sibylle de Brienne, Abbess of Ramerupt
Alix de Brienne
Philippa died on 20 December 1250, a little more than six years after her husband. She was aged about fifty-three.
