World number one Sinner has now completed the 'Golden Masters' by winning all of the ATP's top-ranked events after becoming the first Italian champion at the Foro Italico since Adriano Panatta 50 years ago.
Only Novak Djokovic had previously won all nine Masters 1000 events before Sunday, but there was little doubt about Sinner triumphing over the last 10 days.
Sinner heads into Roland Garros, which starts next weekend, on a 29-match winning streak after beating Ruud for a fifth time in as many meetings.
"There was a lot of tension you know, on both sides and (it) was not perfect, perfect tennis from both of us," said Sinner.
"But I'm really, really happy, it's been an incredible last two-and-a-half months."
And his run of match wins is even longer - 34 in Masters 1000 tournaments - another record he has established in a season in which he has dominated the men's tour.
Sinner can complete his collection of Grand Slams at Roland Garros and with his great rival Carlos Alcaraz out of action few would bet against him securing a first title on Paris clay.
Ruud has won more matches and tournaments on clay than anyone else on the men's tour since the start of 2020 -- last winning a Masters 1000 event at Madrid last year -- but he couldn't beat Sinner for the first time.
Norwegian Ruud had never won a set against Sinner in any of their previous four meetings, but immediately improved on the fearful hammering he received here from the Italian last year by winning the first two games.
But Sinner broke straight back and took the lead in the match after an opening set in which world number 25 held his own against a player he'd previous said "cannot lose".
Sinner then broke Ruud again at the start of the second set and from there it was just a matter of time before he won the championship, even though Ruud performed with credit in front of a packed centre court crowd.
"I know that in football it's a different story," joked Ruud, whose country will play in a World Cup for the first time since 1998.
Norway reached this summer's World Cup in the United States, Canada and Mexico at the expense of Italy, who in March failed for a third consecutive time to qualify for the global showpiece.
"I never played the big three in their prime... But I'm sure Roger, Novak, Rafa, 25, 26 years old was also the same feeling for the other players," said Ruud of Sinner to reporters afterwards.
"I don't see him getting any worse, unfortunately. You just have to think that you have to be better and better because he's also going to get better and better."
It was a good day for Italian tennis as Simone Bolelli and Andrea Vavassori also won the men's doubles title, beating second seeds Marcel Granollers and Horacio Zeballos 7-6(8), 6-7(3), 10-3.