Isnart held land in Agoult, Pontevès, and Entrevennes, from which he took his name.
On 22 November 1251 an Isnart d'Entrevenas witnessed the peace treaty between Barral of Baux and Charles of Anjou, but it was probably not the troubadour but his son.
Isnart's work is preserved in two chansonniers, named D (the Poetarum Provinciali) and N (the Philipps Manuscript).
He wrote two coblas (in series) attacking Blacatz, sometimes classed as a sirventes.
The second cobla goes: "Bertelai" is a reference to the Bertolai of Arthurian legend, who appears in Lancelot du Lac.