He was the first prince of Salerno from 1463, as well as the count of Marsica and Sanseverino, baron of Cilento and lord of Agropoli and Castellabate.
After a momentarily alliance with the Angevines, he sided again for the Aragonese, fighting against the Orsini near Cosenza and conquering Salerno in 1461.
As commander of their fleet, on 7 July 1465, he was victorious with Alessandro Sforza in the battle of Ischia against John II of Lorraine, who had occupied the island.
Roberto Sanseverino was a patron of the arts, having novelist Masuccio Salernitano and Luigi Pulci at his service.
His other son and heir Antonello (it), considered the second prince of Salerno, was one of the leaders of the Conjure of the Barons against the Aragonese.