The 24-year-old midfielder will cost Napoli £6million.
“I am so proud of this choice,” said Datolo. “I have not yet spoken to [Diego Armando] Maradona, but I did speak with [Ezequiel] Lavezzi and [German] Denis.
“They told me all about Napoli and its passionate fans. I am very happy, as I’m going to play for the team that had Maradona.
“I hope to wear this shirt as I make it into the Argentina squad. I cannot wait to get on the field.”