Gianluigi Donnarumma saved Jadon Sancho and Bukayo Saka’s spot kicks after Marcus Rashford hit the post for England in the shoot out.
He clinched a 3-2 victory – following a 1-1 draw after extra time – despite Jordan Pickford denying Andrea Belotti and Jorginho from the spot.
Luke Shaw had put England in dreamland after just two minutes at Wembley but Leonardo Bonucci levelled for Italy in the second half.
Mancini has now guided Italy to their first European Championship title since 1968 and he was overcome at the final whistle.
“We don’t even realise what we have managed to achieve,” said the former Manchester City boss.
“We are delighted for people and the Italian public because they really deserve this after what has been a trying period. This is great joy for us.
“I cried on this ground 30 years ago after the 1992 European Cup final (when Sampdoria lost to Barcelona). That really hurt back then.
“Winning the European Championship for the first time since 1968 and bringing home the trophy I do think it is something incredible.
“It (crying) was the emotion which happens after achieving something incredible. It was the emotion of seeing the guys celebrate and the fans in the stands.
“Seeing everything we have managed to create, all of the hard work we have put in over the last three years but specifically the last 50 days which have been very hard.
“It’s the fact we have been able to forge this team spirit over the last 50 days, they have really created something which can never be separated going forward. They will always be synonymous with this triumph.”
Shaw fired England ahead after just one minute and 57 seconds when he smashed in Kieran Trippier’s far post cross for the fastest goal in a Euro final.
But the Three Lions failed to maintain their energetic start and Italy, who lost to Spain in the 2012 final, slowly got to grips with the game.
Jordan Pickford saved well from Federico Chiesa before Bonucci bundled in from close range after the Everton goalkeeper turned Marco Verratti’s header onto the post.
Mancini said: “I’m very happy because the team played well and we deserved the victory, the goal did cause us a few issues in the first 15 minutes but then we started to take control of the game.
“We were disappointed we had to dig in and go all the way to penalties but we are very happy for Italians everywhere.”
The teams could not be separated after 120 minutes and after Domenico Berardi scored, Harry Kane netted before Pickford saved from Andrea Belotti.
Maguire scored but Rashford and Sancho – who were late substitutes to take penalties – failed from the spot.
Bonucci and Federico Bernardeschi converted and, after Pickford thwarted Jorginho, Saka was denied by Donnarumma to hand the title to Italy.
Mancini added: “We are very fortunate to have Donnarumma, I was sure he was going to save a couple of penalties because he is the best goalkeeper in the world. He really is a wonderful guy and incredible goalkeeper.”