The Genoa-based club have confirmed they have secured the services of the talented attacker on a temporary basis
The 18-year-old, who came through the club's youth system, made his professional debut for the Rossoneri in a Champions League group match against Zenit St Petersburg on December 4, 2012, which his team lost 1-0.
He was included in the senior squad full-time at the beginning of this campaign and played his first Serie A match on August 24 against Hellas Verona, where Massimilano Allegri's men were handed a 2-1 defeat.
"I spoke with [Antonio] Nocerino and [Giampaolo] Pazzini," Petagna told Tuttomercatoweb. "They both advised me to choose Sampdoria.
"They spoke well of boss Delio Rossi and I'm really happy. Now I want to feature as much as I can with the Doria jersey."
Petagna could make his first appearance for his new club in the derby against Genoa, which will be taking place on September 15.
Sampdoria will have the option acquire 50 per cent of the rights for the Italy Under-19 international in the future.