 He was twice appointed as vicar-general for the twin duchy of Athens and Neopatras, in 1359–61 and again 1363–66.The latter appointment came after the "de facto" ruler of the duchies, the marshal Roger de Llúria, had admitted a Turkish garrison into Thebes to strengthen his own position.The inhabitants of the duchy sent a delegation to the King, who in August 1363 appointed Matthew to the post—reportedly for life—with the task of restoring order.