Senad Lulic grabbed the only goal, slotting home with just 19 minutes remaining to spark wild celebrations in one half of the capital.
Both sides had played their part in a predictably frenetic opening to the game that resulted in early bookings for both Cristian Ledesma and Federico Balzaretti.
Lazio could have been ahead inside the opening four minutes, but Miroslav Klose fired into the side netting after Bogdan Lobont had been unable to hold onto a low strike from the dynamic Lulic.
Roma then could have taken the lead soon after when Erik Lamela and Marquinho combined to put Michael Bradley in on goal, only to see the American's subsequent strike trickle wide after he made a late run into the center of the box.
For the majority of the half, the Giallorossi looked the side most likely to make the breakthrough, but, for the most part, they were restricted to long-range efforts from Francesco Totti and Lamela. In the end, they were lucky to go in level at the break, with Klose surprisingly heading straight at Lobont after being picked out at the back post by Stefan Radu's deep cross from the left-hand side.
Moments later, the Germany international became the fifth player to enter the book, which merely underlined the fractious nature of a first half that ended just second after Mattia Destro had got his first sight of goal, with the striker just failing to climb high enough to get a clean connection on a brilliant cross from Marquinhos.
The Giallorossi continued to press in the secnod half, and Totti tested Federico Marchetti with a decent low strike before the Lazio goalkeeper was called upon again to get down low to stop a snap-shot from Destro.
A goal was coming - but it arrived at the other end, with Lulic tapping home at the back post after Lobont had deflected Antonio Candreva's cross into his path.
Roma tried to rally, throwing striker Pablo Osvaldo on in place of left back Federico Balzaretti, but it did not truly come close to forcing an equalizer. Indeed, it was Lazio that looked the more likely to net the game's next goal, with Lobont denying Stefano Mauri in an injury-time one-on-one.
In the end, though, Lulic's goal proved sufficient to earn the Biancocelesti their first meaningful piece of silverware since lifting the same trophy four years ago, while Bradley and his Roma teammates were denied a place in Europe following a sixth-place finish in Serie A.
