Sexton will partner Simon Keogh at half-back for the clash with the Exiles, who have been drawn with Leinster in Pool 6 for this season's Heineken Cup.
Fergus McFadden will line alongside Shaun Berne at centre and Isa Nacewa reverts to the left wing after starting at centre in last week's 38-10 victory over Rugby Nice Côte d'Azur.
Sean O'Brien will start in the back row alongside Shane Jennings and number 8 Stephen Keogh, who captained the province in that Nice win.
There are still tickets available for Friday's game from Spar (Donnybrook) and the Leinster Rugby Store and cash will also be taken at the turnstiles.
Meanwhile, match sponsors OZO will be running a 'face in the crowd' competition.
Any supporters wearing either the new Leinster home or away jersey are in with a chance of winning one of six €50 vouchers for the Leinster Rugby Store.
An Ozo representative will be on the lookout around all four sections of the ground. Wear your colours with pride and you could be a winner!
LEINSTER (v London Irish) - Niall Morris; Shane Horgan, Fergus McFadden, Shaun Berne, Isa Nacewa; Jonathan Sexton, Simon Keogh; Ronan McCormack, Bernard Jackman, Stan Wright, Leo Cullen (capt), Devin Toner, Sean O'Brien, Shane Jennings, Stephen Keogh.
Replacements (from): John Fogarty, Jason Harris-Wright, Cian Healy, Mike Ross, Malcolm O'Kelly, Eoin Sheriff, Kevin McLaughlin, Chris Keane, David Moore, Paul O'Donohoe, Billy Ngawini, Brendan Macken, Girvan Dempsey.