The 27-year-old Portuguese had reportedly attracted the interest of Barclays Premier League outfit QPR but, after completing a medical at Castelvolturno, he opted instead to help Napoli in their bid for the Scudetto.
He told sscnapoli.it: "I'm really happy to wear this shirt. I wanted to join Napoli because it's a big club with a lot of great players.
"I've heard a lot about the passionate fans and I can't wait to experience a game at the Stadio San Paolo."
After joining Porto from Belenenses in 2008, Rolando played a key role as the Dragons won three Portuguese championships in four years and claimed the Europa League trophy in 2011.
Napoli have also allowed Bruno Uvini to join Siena until the end of the season, with fellow defender Federico Fernandez joining Primera Division side Getafe in a similar arrangement.