On 17 December 1384 "Roman" pope Urban VI appointed him cardinal deacon of the church of San Adriano.
Fieschi served as the legate of Pope Boniface IX in Genoa and Campania.
Around 1403/04, however, he began to distance himself from this pope, which was related to the change of direction of his homeland, Genoa.
He did not attend the Council of Pisa (1409), but recognised Pope Alexander V, thus leaving the Avignon obedience.
He served as the legate of Alexander's successor John XXIII in Bologna and Ferrara.