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to Dublin for the game.
Typically, the pace was frantic in the early stages — showcasing the contrast in styles of both teams.
The Scarlets looked for width, while a line-out rumble from the Munster pack made good yardage.
It was the Irish province who took a seventh-minute lead through a Tyler Bleyendaal penalty, but that was the last time they got anywhere close.
The Scarlets were up and running with a corner try for the departing Liam Williams after a perfectlyweighted cross kick from Rhys Patchell and never looked back after that.
Patchell slotted a penalty to extend the lead to 8-3 then Steff Evans finished off a try-of-the-season contender.
A slick pass from Beirne freed Jonathan Davies deep in his half, the British Lion put Evans away and the pair exchanged passes for the youngster to dive over for his 13th league try of the campaign.
It was sublime stuff from Pivac’s men, defying the greasy conditions and blustery wind sweeping around the Aviva.
They should have had another after Evans was sent racing down the left wing only for Gareth Davies to spill a pass with the line beckoning.
Davies, though, made up for his lapse moments later, taking an inside pass from Scott Williams after another defence-splitting intervention from the outstanding Evans.
The final pass to the international scrum-half appeared forward, but the television match official thought otherwise and the score was given.
There was more to come, plenty of it.
The clock had barely ticked to the half hour mark and the Scarlets were celebrating their fourth try.
This time it arrived via close quarters, with former Leinster lock Beirne twisting over against his countrymen.
A Bleyendaal try on the stroke of half-time served as a necessary reality check for those already dancing on cloud nine, but even for a side of Munster’s history, there remained a mountain to climb.
That got bigger when Patchell landed a penalty four minutes after the restart and another Munster miracle never materialised.
With the second half peppered with loose kicks and Munster delivering one fumble after another, the Scarlets’ lead was never remotely threatened.
DTH van der Merwe’s score provided the prompt for the Munster fans to head for the exits, and after Munster wings Andrew Conway and Keith Earls claimed late consolations, it was James Davies who raced away to complete the triumph with John Barclay and Ken Owens lifting the trophy amid jubilant scenes.