A second trophy this season
Joe Schmidt bowed out after three years in charge of Leinster before taking over the Ireland reins with a Pro12 triumph thanks to a 24-18 triumph over Ulster in Dublin.
The New Zealander added a second trophy this season to the European Challenge Cup won two weeks ago as he took his total haul with the Irish province to four trophies.
Having won the European Cup in his first two seasons, he added the two other trophies available to Leinster this campaign, ending a run of three successive defeats in Celtic League finals for the province.
Shane Jennings and Jamie Heaslip scored tries for Leinster while Jonathan Sexton, in his last game before moving to Racing Metro next season, kicked a conversion and four penalties.
South African Ruan Pienaar kicked six penalties for Ulster in a fiercely competitive clash.
It was Leinster's third Celtic League title while Ulster remain on one success, in 2006.
Leinster flew out the blocks and scored the first try of the match after just three minutes - the newly crowned Challenge Cup champions rewarded for an early show of intent.
Sexton turned down a shot at the posts and instead kicked for the corner and Leinster produced a textbook drive after collecting the line-out, Jennings the man who dotted down.
Sexton kicked the conversion from the corner and it wasn't long before he extended his side's lead to 10-0 with Chris Henry failing to release his man, capping a chaotic early period for a stunned Ulster.
That stirred the Ulstermen into action however and some concerted pressure in the left-hand corner almost resulted in a try, only for Leinster to withstand the barrage.
On 18 minutes, Ulster missed a glorious chance to get back into the match after British and Irish Lions winger Tommy Bowe burst infield and when Darren Cave spun the ball wide to Robbie Diack, he had the simplest of finishes but Leinster got back to hold him up over the line.
On 25 minutes, Ulster finally got themselves on the scoreboard, Pienaar making no mistake from the tee but Sexton responded in kind soon after to restore his side's ten point advantage.
Again Ulster came back and Pienaar made it two from two on 36 minutes but Sexton notched a crucial penalty on the stroke of half-time, ensuring Leinster earned themselves some breathing space at the interval.
Things weren't going Ulster's way and Leinster threatened to build an unassailable lead when Diack was sent to the sin bin on 44 minutes for going off his feet but then Ireland flyhalf Paddy Jackson sparked the hosts for the day into life.
He scythed his way through the middle but didn't have the support required to make sure of the try, however Isa Nacewa, in his last game before retirement, was adjudged to have made a high tackle on the 21-year-old and he was shown a yellow card.
Pienaar slotted the simple penalty from in front of the posts to make the score 19-9 but with both sides down to 14.
Ulster could sense a way back into the contest and, with the wind in their sails, Pienaar trimmed the gap to seven when a superb chase from Bowe saw Leinster infringe and concede the penalty on 50 minutes.
With Diack back on the pitch but Nacewa yet to return, Pienaar brought Ulster to within four points, the closest they had been since Jennings' third-minute try, but Leinster came back, aware that they were losing momentum.
And it was Heaslip, who the help of lock Devin Tower, who burrowed his way over for another try that was borne out of forward grunt in the corner.
Sexton missed the conversion, ensuring Ulster weren't out of it, nine points down and after more good work from the impressive Rory Best, they were back to within a converted try after an enormous kick from the flawless Pienaar on 69 minutes.
With three final defeats in the last three years, Leinster were getting nervous and Ulster almost cut them open with seven minutes left on the clock, only for a knock-one at the crucial moment to cost them dearly.
Awarded a kickable penalty with four minutes left on the clock, Pienaar opted to kick for the corner and despite numerous phases in Leinster territory, Ulster conceded the penalty.
Leinster marched the play downfield and allowed the clock to tick down before Brian O'Driscoll kicked the ball out to rubber-stamp his side's victory.
Pens: Pienaar 6
Tries: Jennings, Heaslip
Pens: Sexton 3
Ulster: 15 Jared Payne, 14 Andrew Trimble, 13 Darren Cave, 12 Stuart Olding, 11 Tommy Bowe, 10 Paddy Jackson, 9 Ruan Pienaar, 8 Nick Williams, 7 Chris Henry, 6 Robbie Diack, 5 Dan Tuohy, 4 Johann Muller (captain), 3 John Afoa, 2 Rory Best, 1 Tom Court.
Replacements: 16 Rob Herring, 17 Callum Black, 18 Declan Fitzpatrick, 19 Iain Henderson, 20 Mike McComish, 21 Paul Marshall, 22 Michael Allen, 23 Peter Nelson.
Leinster: 15 Rob Kearney, 14 Fergus McFadden, 13 Brian O'Driscoll, 12 Ian Madigan, 11 Isa Nacewa, 10 Jonathan Sexton, 9 Isaac Boss, 8 Jamie Heaslip, 7 Shane Jennings, 6 Kevin McLaughlin, 5 Devin Toner, 4 Leo Cullen (captain), 3 Mike Ross, 2 Richardt Strauss, 1 Cian Healy.
Replacements: 16 Sean Cronin, 17 Jack McGrath, 18 Jamie Hagan, 19 Quinn Roux, 20 Rhys Ruddock, 21 John Cooney, 22 Andrew Goodman, 23 Andrew Conway.
Referee: John Lacey (Ireland)
Assistant Referees: George Clancy, Peter Fitzgibbon (both Ireland)
TMO: Dermot Moloney (Ireland)