Mahieu le Juif was an Old French trouvère. His name means "Matthew the Jew" and, if his own songs are to be believed, he was a convert from Judaism to Christianity. Only two of his songs survive, one with a melody. He has been conflated with Mahieu de Gant, but the same manuscript that contains both their works clearly distinguishes them.
Mahieu's more popular song, Par grant franchise, was very widely copied and today it exists in twelve chansonniers, including one in Occitan. It was probably the subject of the song that accounts for its popularity. Mahieu abandoned the faith of the Jews for that of his Christian lady. Expecting to receive praise, however, he got only ridicule. The apropos melody of this song survives in many variations, but all are of a simple, yet tight, structure. There is intertextual similarity between a piece of the troubadour Albertet de Sestaro and Par grant, but the direction of any influence of the one on the other cannot be ascertained: though Jeanroy thought the trouvère was influenced by the troubadour.
Mahieu's other piece, Pour autrui movrai, likewise refers to his Jewishness, but it was not as widely read.