In 1439, he received an appointment as antipope, which he accepted (under the name of Felix V), although he subsequently resigned a decade later out of a fear of undermining the religious unity of Christians.
Aastal 1439 sai ta nimetamise vastupaavstiks, millega ta nõustus (Felix V nime all), kuigi ta seejärel kümmekond aastat hiljem sellest loobus, kartuses õõnestada kristlaste usulist ühtsust.