Leinster will contest two major finals in the coming weeks after ending Ulster's Magners League title aspirations with an 18-3 win in the semi-final at the RDS.
Fergus McFadden's 25th-minute effort was the only try of a tightly-contested first half, supplemented by two Jonathan Sexton penalties to give the hosts an 11-0 half-time lead.
A monster penalty from Ruan Pienaar got Ulster off the mark, but Luke Fitzgerald's late converted try leaves Leinster just 160 minutes away from a potential Magners League and Heineken Cup double.
But they have a few injury concerns, including Brian O'Driscoll after the centre was taking off after suffering a a leg injury just eight days before they face Northampton at the Millennium Stadium in the Heineken Cup final.
Leinster quickly got on the front foot, a lovely improvised pass from O'Driscoll sending Sean O'Brien storming into the 22 and Sexton clipped over the ensuing penalty.
The men in blue kept the pressure on, opting for a close range scrum from a penalty and, with Ulster caught short for defenders out wide, O'Driscoll and Isa Nacewa put McFadden over in the right corner and Sexton extended the advantage with another penalty right on half-time.
With 18 minutes remaining, Pienaar opened Ulster's account with a stunning penalty goal from close to the visitors' 10-metre line.
The next score was hugely important and it went to Leinster, with Fitzgerald worming his way past Pienaar and Pedrie Wannenburg before showing great pace to scoot in under the posts.
McFadden converted and Ulster's late series of attacks went unrewarded as Leinster booked their spot in the May 28 decider for a second successive Magners League final appearance.