The 29-year-old goalkeeper will provide competition for number one Djordje Petrović at the Vitality Stadium, having completed his medical before finalising a season-long switch to the south coast.
Bournemouth will not pay a loan fee for Di Gregorio but will cover his full salary for the duration, with a £1million penalty applying if the option to sign him permanently for £12million, plus a further £2.5million in add-ons, is not exercised at the end of the season.
Di Gregorio, an Inter Milan academy product who went on to make more than 100 Serie A appearances and 14 in the Champions League, expressed his delight at the move.
"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," he said. "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."
Tiago Pinto, Bournemouth's President of Football Operations, welcomed the goalkeeper's arrival as a significant addition to the squad.
"Michele is a goalkeeper with excellent qualities and valuable experience at the highest level. He has consistently demonstrated his ability in Serie A and in European competitions, and we believe he will be an excellent addition to our squad," Pinto said.
The move brings an end to Di Gregorio's time as Juventus's first-choice goalkeeper after just over a year in Turin, with the Bianconeri having signed Guglielmo Vicario on loan from Tottenham Hotspur as his replacement. Juventus originally paid an initial loan fee before making the transfer permanent for a total outlay in the region of €18million, meaning a Bournemouth buy-out next summer would allow the Serie A club to recoup much of their investment.
Di Gregorio's arrival is expected to be Bournemouth's final piece of business of the summer, following the permanent signings of forward Álvaro Rodríguez from Elche, defender Antonio Silva from Benfica and full-back Juanlu Sánchez from Sevilla.
His arrival paves the way for back-up goalkeeper Will Dennis to pursue a fresh loan opportunity after a season spent with Leyton Orient in League One.