The 29-year-old joins after establishing himself as one of Serie A’s top goalkeepers.
Di Gregorio began his career at Inter Milan before loan spells with Renate, Novara and Pordenone.
He was named Serie A’s Best Goalkeeper for 2023/24 after keeping 14 clean sheets in 37 appearances.
“I’m very happy to be here. This is a very important moment for me and that's why I think the decision to come here to Bournemouth was the right one,” Gregorio told Bournemouth website.
“I felt the club's desire to have me here and I felt the ambition that this club has to continue to grow and do great things.
“The Premier League is the most beautiful league in the world. It's an honour for me to be here and to have the chance to play and play at such a high level.”