In 1419 he accompanied Cardinal Branda da Castiglione, who thought highly of him, on his difficult mission to Germany and Bohemia, where the Hussites were in open rebellion. He also served as a papal envoy to England. In 1426 Martin V created Cesarini a cardinal and later sent him to Germany to preach a crusade against the Hussites. After the crusade failed, Cesarini went to Basel to preside over the council that had begun there.