He his not the first... edit

The first chroniclers to write in french did it about 125 years before him, but still come from flemish regions. Also, the Grandes chroniques de France, where written in french in the second half of the XIIIth century.

About this subject, see Gabrielle M. Spiegel, Romancing the Past: The Rise of Vernacular Prose Historiography in Thirtheenth-Century France, Berkeley: California University Press, 1993.