A record European Cup Final crowd of 81,774 watched another outstanding performance from the Dubliners who were simply too strong, too skilful and too good for their well-defeated rivals.
Leinster started this private Irish knees up in London as favourites but it was their rivals who drew first blood with early points on the board.
The hungry men from the North applied plenty of pressure from the kick off, forcing Leinster back on their heels and eventually conceded an early penalty with Ruan Pienaar kicked for a 3-0 lead.
But it did not take very long for the reigning champions to switch up a gear or two and a strong forward surge in the 13th minute resulted in flanker O'Brien just managing to touch the ball down on the white line as he was tackled.
Welsh referee Nigel Owens asked for official confirmation from upstairs and television replays showed the forward had scored a try which Jonathan Sexton converted.
Sexton missed a penalty moments later as the game opened up for a spell of thrilling, flowing running rugby with both sides anxious to run the ball at every opportunity.
Sexton went close but was tackled before he reached the Ulster line and the white-shirted defence had to fly to the other side of the field to stop another Leinster attack as the pressure was turned up.
A superb Brian O'Driscoll inside pass after a mini-break in midfield opened up the Ulster defence, and the ball was finally switched to Healy who was tackled on the line but his momentum enabled him to ground the ball for a second try. Sexton converted for a 14-3 lead after 32 minutes.
Ulster failed to make their heavy pressure toll when Paddy Jackson hooked a drop goal attempt wide left. A stunning 50 metre penalty from Pienaar gave them hope on the stroke of half-time as then went into the break eight points adrift.
Leinster piled on the pressure at the start of the second half with another forward-dominated move ending with referee Owens awarding a penalty try as Ulster deliberately collapsed a maul inches from their line.
Sexton converted for a convincing 21-6 lead.
Ulster withdrew hapless fly-half Jackson from the front line and replaced him with experienced Ian Humphreys.
But you sensed the game had already slipped through their fingers and Leinster were in full command.
Pienaar and Sexton exchanged further penalties before Ulster finally broke through the thick blue line of defence.
Constant pressure from one side of the field to the other eventually saw the ball floated from Paddy Wallace to Tuohy and the big second row man dived for a try on the hour.
Sexton's second penalty of the game stretched Leinster's lead to 13 points with 10 minutes remaining. Replacement Humphreys had to be replaced himself by Paul Marshall when he was injured.
Ulster had full-back Stefan Terblanche sent to the sin bin for a bad off the ball tackle and Sexton kicked a third penalty before a fourth try in the final minute from replacement hooker Sean Cronin finished the job.
Final Score Leinster (IRL) 42 Ulster (IRL) 14
Tries - O'Brien, Healy, penalty try, van der Merwe, Cronin
Conversions - Sexton (3), McFadden
Penalties - Sexton (3)
Tries - Tuohy
Penalties - Pienaar (2)
Drop goal - Pienaar
Yellow card Terblanche (dangerous tackle 73min)
Leinster: Rob Kearney, Fergus McFadden, Brian O'Driscoll, Gordon D'Arcy, Isa Nacewa, Johnny Sexton, Eoin Reddan, Jamie Heaslip, Sean O'Brien, Kevin McLaughlin, Brad Thorn, Leo Cullen (capt), Mike Ross, Richardt Strauss, Cian Healy
Replacements: Sean Cronin, Heinke Van der Merwe, Nathan White, Devin Toner, Shane Jennings, Isaac Boss, Ian Madigan, Dave Kearney
Ulster: Stefan Terblanche, Andrew Trimble, Darren Cave, Paddy Wallace, Craig Gilroy, Paddy Jackson, Ruan Pienaar, Pedrie Wannenburg, Chris Henry, Stephen Ferris, Dan Tuohy, Johann Muller (capt), John Afoa, Rory Best, Tom Court
Replacements: Nigel Brady, Paddy McAllister, Declan Fitzpatrick, Lewis Stevenson, Willie Faloon, Paul Marshall, Ian Humphreys, Adam D'Arcy