He successfully faced a plot against him in the city. However, after treason of his nephew Nicolò da Carrara who had sided with the Scaliger of Verona, Marsilio was forced to relinquish Padua to Cangrande della Scala in 1328. He retained the title of vicar for the city, and managed to marry Jacopo's daughter Taddea to Mastino II della Scala. In the war against the Papal States, he warred alongside the latter at Brescia in 1330/1331, conquering the city by treason. In the following years he acted as vicar of Brescia. In 1332 Marsilio had his wife Bartolomea Scrovegni poisoned, suspecting she was unfaithful.