Ermessende first married Pierre Bermond, lord of Anduze, and they ruled Melgueil from 1170 to 1172 when he died.
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Ermessende died in 1176; her will, made shortly before, was heard before the cardinal deacon Raymond des Arènes, Aldebert, bishop of Nîmes, Bernard Ato V, viscount of Nîmes and Agde, and Gui Guerrejat, guardian of William VIII of Montpellier.
In 1177 she joined Gui Guerrejat (the lover of Azalais de Porcairagues), Bernard Ato V of Nîmes and Agde, and Gui's nephews William VIII of Montpellier and Gui Burgundion, in an alliance in opposition to Raymond VI of Toulouse, whose power suddenly increased when he became ruler of Melgueil as widower of Ermessende of Pelet.