Clinical Wales rose to the occasion with the roof open and rain lashing down in Cardiff to end a six-year wait for a Six Nations title and claim a first clean sweep since 2012.
Hadleigh Parkes set the tone with an early try that was set up by the excellent Gareth Anscombe, who was on target with three penalties to give Wales a 16-0 half-time advantage.
Indisciplined Ireland was a shadow of the team that pulled off a Grand Slam last year and Wales took full advantage, Anscombe adding another three penalties in the second half in a perfect kicking display to take his tally to 20 points.
Nothing went right for disjointed Ireland as it relinquished its title with a whimper, Gatland, who will end his long reign after the Rugby World Cup later this year, becoming the first coach to mastermind three Grand Slams in the tournament.
Ireland, which scored a late consolation through Jordan Larmour, finished third behind England in its final Six Nations with Joe Schmidt in charge, while magnificent Wales's winning run now stands at 14 matches after it got the job done in emphatic fashion.
Wales eased the nerves by making a dream start, all-action centre Parkes plucking Anscombe's deft kick over the top to score inside two minutes.
George North made an early exit with a wrist injury and Alun Wyn Jones had treatment on his knee, but a long-range penalty from Anscombe, shifted to full-back with Dan Biggar on at five-eighth and Liam Williams moving to the wing, extended the lead.
Ireland applied some pressure but a rock-solid Wales defence kept it scoreless and Anscombe punished indiscipline from the defending champion with two penalties to put Gatland's men 16-0 up at the break.
Composed Wales carried on where it left off after the interval, Anscombe again making no mistake again from the tee after Cian Healy was deemed to have come from the side of a maul.
Ireland continued to struggle in tricky conditions, summed up when Johnny Sexton threw a pass straight into touch in a promising situation after the holder was finally able to put phases together.
There was no let-up from a relentless Wales, led by the immense Jones, and two more Anscombe strikes put the hosts well out of sight.
Ireland finally breached the Wales defence when Larmour stepped outside to score after the ball was moved swiftly from left to right and Jack Carty added the extras, but the Welsh Victory party was already under way by then.