After a tightly-contested first half, the Partenopei hit the Bianconeri with strikes from Edinson Cavani and Marek Hamsik after the break, as Walter Mazzarri's men extinguished the Old Lady's hopes of a double on Alessandro Del Piero's farewell game for the Turin giants, while also sending Antonio Conte's side to their first defeat of the season.
Napoli got off to a wonderful start, as in the third minute Camilo Zuniga found himself unmarked on the end of a great cross by Hugo Campagnaro, but saw his close-range header tipped wide by Juventus goalkeeper Marco Storari.
Moments later, Napoli created another superb chance when Ezequiel Lavezzi released Cavani with a exquisite pass after winning the ball from Arturo Vidal, but the Uruguayan was flagged for offside just as he was about to pull the trigger.
Juventus' answer came through Claudio Marchisio in the 19th minute, when the midfielder collected an Alessandro Del Piero finish, which was blocked by Napoli's defence, and struck the ball from well outside the box, only to see his powerful drive saved by Morgan De Sanctis.
Just before the half-hour mark the Partenopei almost got the opener when Hamsik fell one step short of connecting with a floating cross by Lavezzi at the left post, much to the relief of the Juventus faithful.
The last minutes of the first half belonged to Juventus as Marchisio and Del Piero tested De Sanctis, but the goalkeeper stood strong to deny the duo.
Both teams employed conservative tactics in the beginning of the second half as the game became increasingly scrappy. Blerim Dzemaili created a superb chance for Napoli in the 50th minute when he whipped in a cross, which Cavani just could not connect with in the centre of the box.
The Partenopei would not wait long for the opener, however, as just after the hour mark Lavezzi found himself behind Juventus' defence only to be taken down in the penalty area by Bianconeri goalkeeper Storari.
Cavani stepped up to convert the resulting spot-kick, sending a powerful low effort in the right corner to give Napoli a deserved lead. This was the Uruguayan's fifth goal in Coppa Italia this season, securing the striker as the top scorer of the competition.
Juventus tried to get back into the game, but were struggling to to create chances after the opener as the Partenopei valiantly held off the Old Lady's advances. Coach Antonio Conte decided to withdraw Del Piero in the 68th minute as the curtain fell on the legendary striker's illustrious career with the Bianconeri.
The tireless Vidal almost drew the game level shortly after, but was denied by former Juventus goalkeeper De Sanctis, who did well to parry the Chilean's thunderous volley at the right post.
In the 74th minute Simone Pepe was rather unfortunate to see a goal-bound finish deflected from its path as the Old Lady were tightening the grip. But despite their best efforts, the Bianconeri were unable to break down Napoli in the remaining time, and were punished for their overcommitment in attack with another goal.
A quick break saw Goran Pandev release Hamsik in a one-on-one with Storari, and the attacker made no mistake as he slipped the ball past Storari to bring Juventus to their first loss in their 2011-2012 campaign.
To add to the Bianconeri's misery, Fabio Quagliarella was sent off in the final minutes of the game for elbowing Salvatore Aronica as the Old Lady's capitulation was complete.
The victory saw the Partenopei lift the Coppa Italia for their first piece of silverware in 22 years.