Title-holders India, set 339 to win, collapsed to 33 for three and 54 for five against a Pakistan side they had thrashed by 124 runs in their tournament opener at Edgbaston on June 4.
They were eventually dismissed for 158 in reply to Pakistan s 338 for four, which featured Fakhar Zaman s 114, the left-handed opener s maiden one-day international hundred coming in just his fourth match at this level.
Amir, who missed Pakistan s eight-wicket semi-final win over England with a back spasm, finished with three wickets for 16 runs in six overs.
But it was fellow paceman Hasan Ali, the player of the tournament having kick-started Pakistan s revival in their group win over South Africa, who ended the match with more than 19 overs left when he had Jasprit Bumrah caught by gleeful captain and wicket-keeper Sarfraz Ahmed.
Left-arm fast bowler Amir, whose career was almost ended on the other side of London s River Thames by a ban and jail term he received for his part in a spot-fixing scam during a 2010 Test against England at Lord s, was superb.
He dismissed three of the world s top (ODI) batsmen in Rohit Sharma (nought), India captain Virat Kohli (five) and Shikhar Dhawan (21) in a stunning new-ball spell.
“It s been an up and down ride for us but I m just so proud of the boys,” Pakistan coach Mickey Arthur told Sky Sports.
“We dusted ourselves off after the defeat to India at Edgbaston and came back superbly,” added the South African after Pakistan s first major global tournament success since they won the 2009 World Twenty20 in England.
An elated Sarfraz added: “After the India match when we lost in the group stage, I told my boys the tournament hadn t finished yet.
“Fakhar is a great impact player, he played like a champion batsman today. Amir bowled brilliantly today but all my bowlers bowled really well.”
This was Pakistan s largest margin of victory, by runs, in 129 ODIs against India, surpassing their 159-run success at Delhi in 2005.
“Rohit, Dhawan and Kohli have been in tremendous form so I was looking for early wickets – and I did it,” said Amir.
Kohli accepted his side had been second best as he acknowledged Pakistan s “amazing tournament”.
“They outplayed us, they were more intense and passionate on the day,” he said.
Amir struck just three balls into India s reply when, after bowling two outswingers to Sharma, he had him lbw with an inswinger.
Then one ball after Kohli, the world s leading ODI batsman, was dropped at slip off Amir, the bowler had him caught at point by Shadab Khan.
The collapse continued when left-handed opener Dhawan was caught behind off Amir.
India then lost two wickets for no runs in four balls to be 54 for five inside 14 overs.
Yuvraj Singh was lbw to leg-spinner Shadab and former captain MS Dhoni, the hero of many an India rescue mission, holed out in the deep.
Pakistan, who had lost all three of their previous matches against India in the knockout stages of International Cricket Council tournaments and started this event the lowest ranked of the eight teams involved, were now on the brink of a sensational win.
Hardik Pandya cheered India fans in a capacity crowd as he hit three sixes off succesive balls to bring up a dashing fifty.
But he only looked to be delaying the inevitable and a mix-up with Ravindra Jadeja saw him run out for 76.
Earlier, Fakhar rode his luck after Kohli sent Pakistan into bat at a sun-drenched Oval.
He would have been run out for one if Kedar Jadhav s throw from cover had hit and he was caught behind off a Bumrah no-ball on three.
Fakhar, the man-of-the-match, shared an opening stand of 128 with Azhar Ali (59).
But the run-out Pakistan s openers had threatened arrived when Fakhar s failure to respond to Azhar s call saw the former ODI captain fall by a distance.
The 27-year-old Fakhar, however, put the setback behind him to complete a 92-ball hundred when he swept star off-spinner Ravichandran Ashwin for his 12th four.
He was eventually out when he sliced medium-pacer Pandya to Jadeja, running back from point.
But veteran all-rounder Mohammad Hafeez s quickfire 57 not out, including three sixes, then took Pakistan well beyond 300.