Cullen, who lines up alongside Scotland's Nathan Hines in the second row, is one of six Ireland internationals in a pack which includes Sean O'Brien who has scored four tries to date in this season's Heineken Cup.
O'Brien is joined in the back row by Kevin McLaughlin and fellow ERC Player of the Year award nominee Jamie Heaslip.
Meanwhile, Ireland duo Cian Healy and Mike Ross will scrum down alongside Richardt Strauss in a tried and trusted front row unit.
Brian O'Driscoll, who has now scored 30 tries in the Heineken Cup, has proven his fitness and will start at centre after recovering from a knee injury.
Centres O'Driscoll and Gordon D'Arcy are two of the six Ireland internationals selected in the province's back-line.
The tournament's top points scorer Jonathan Sexton partners Eoin Reddan at half-back with Luke Fitzgerald, Shane Horgan and Isa Nacewa forming the back-three.
Shane Jennings' inclusion as a replacement is the only change to the 23-man panel from the semi-final for what will be Leinster's second Heineken Cup final appearance in three years.
LEINSTER (v Northampton Saints): Isa Nacewa; Shane Horgan, Brian O'Driscoll, Gordon D'Arcy, Luke Fitzgerald; Jonathan Sexton, Eoin Reddan; Cian Healy, Richardt Strauss, Mike Ross, Leo Cullen (capt), Nathan Hines, Kevin McLaughlin, Sean O'Brien, Jamie Heaslip.
Replacements: Jason Harris-Wright, Heinke van der Merwe, Stan Wright, Devin Toner, Shane Jennings, Isaac Boss, Ian Madigan, Fergus McFadden.