The 25-year-old arrives from the Tuscany side on a deal reported to be worth $11.3 million.
"I'm happy about my new adventure at a prestigious club like Napoli," Di Lorenzo, who joined Empoli in 2017, told the club's website.
"I can't wait to start the new season and get to know my new teammates in Dimaro."
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A versatile player, who can also play as an attacking wing-back, Di Lorenzo scored five goals in 37 games for Empoli during his first Serie A campaign which just ended.
"Welcome to Napoli Giovanni!" tweeted Napoli owner Aurelio De Laurentiis.
Empoli finished the season equal on points with Genoa but were relegated back to Serie B on inferior head-to-head difference.
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