He was the eighth son of Charles II of Naples and Maria of Hungary (see Elizabeth of Sicily).
In 1309, he received Nocera and Isernia and exchanged Montescaglioso for Sorrento and Castellammare di Stabia.
He began serving his brother, King Robert, against the Ghibellines of Uguccione della Faggiuola in Tuscany.
He celebrated a jubilee at Siena and then moved on to Florence, where he stayed with the Mozzi family and the commune granted him a stipend of 4,000 florins.
At Robert's request, Peter brought reinforcements north and met with initial successes.