The 6ft 4in second row, who turns 25 at the end of the month, led the Limerick men superbly as a combination of their free-running backs and ball-handling forwards saw Shannon run amok in the first half at Lansdowne Road.
Their 25-point first-half haul - with centre Brian Tuohy, flanker Colm McMahon and hooker Nigel Conroy all touching down - was enough to see off 'Quins, who replied with 20 of their own in a wind-assisted second half.
"It's a massive achievement to do the two-in-a-row," admitted a jubilant Hayes. "All credit to Harlequins, they came back at us well. It's fair enough to say we creaked at some stages but we pulled through in the end.
"We used our experience of previous finals well. There's a continuity at Shannon - from the three-in-a-row Munster Senior Cup team in the 1980s to the team in the nineties who won four AILs in-a-row.
"There's always been players coming through from previous teams who have become the experienced heads in the next team. It helps an awful lot."
The 38-year-old, who felt McMahon's opportunistic score was the difference in the end, added: "The wind was a huge factor. We started very well and took our opportunities, kept the ball alive and went for quick rucks.
"I've been at Shannon over 20 years, and it's superb to be involved with a great bunch of lads. They're very ambitious and I was only there to help them out - you saw that the hunger they have out there."
Man-of-the-match Stephen Keogh said: "We came back out in the second half and said to ourselves, 'it's back to nil-all'. We knew 'Quins would come back at us with everything they had.
"This win means a lot to the club and the players. Guys like Eddie Halvey - to see the experienced players with such a will to win and passion, it transfers to the younger guys too," added the Munster back row.