The Italy international has joined the Serie A champions on a season-long loan.
Lucca joined Antonio Conte's team at the Dimaro-Folgarida training camp in Trentino, even before the announcement was made.
And now it's finally official. As usual, Napoli president Aurelio De Laurentiis tweeted: "Welcome Lorenzo ," he wrote.
The player arrives on loan with an obligation to buy from Udinese for a total fee of around €35m.
"SSC Napoli announces that it has acquired the player Lorenzo Lucca from Udinese Calcio on loan with an obligation to buy," reads Napoli's official statement.