Jonny Sexton led the way with a match haul of 22 points as he kicked eight out of eight, while Man of the Match Jamie Heaslip and Brian O'Driscoll scored tries.
But while there was great joy for Leinster and their fans, there was bitter disappointment for Magners League leaders Munster as they lost for only the third time at home in Europe in the semi-finals of the Amlin Challenge Cup.
They were beaten 20-12 at Thomond Park, Limerick, by Harlequins to miss out on a fifth major European final. It was their first home defeat of an otherwise outstanding season.
Munster have already confirmed home advantage in the Magners League Play-Off semi-finals and Leinster will also have a home tie if they can beat Glasgow Warriors at the RDS on Friday night.