McFadden's positional switch caters for the return of Brian O'Driscoll who, having overcome a back injury, starts alongside Ian Madigan in the centre.
Isaac Boss makes his 25th appearance of the season and will partner Jonathan Sexton at half-back, with the Ireland out-half earning his 110th provincial cap (having scored 1,013 points to date).
Up front, Cian Healy and Richardt Strauss return to the starting line-up after coming on as replacements in the Amlin Challenge Cup final victory last weekend.
Kevin McLaughlin, meanwhile, returns to the back row in place of Sean O'Brien (bruised knee) who has failed to recover from injury.
McLaughlin will form an experienced back row unit alongside Shane Jennings, who is set to make his 175th appearance, and number 8 Jamie Heaslip.
LEINSTER (v Ulster): Rob Kearney; Fergus McFadden, Brian O'Driscoll, Ian Madigan, Isa Nacewa; Jonathan Sexton, Isaac Boss; Cian Healy, Richardt Strauss, Mike Ross, Leo Cullen (capt), Devin Toner, Kevin McLaughlin, Shane Jennings, Jamie Heaslip.
Replacements: Sean Cronin, Jack McGrath, Jamie Hagan, Quinn Roux, Rhys Ruddock, John Cooney, Andrew Goodman, Andrew Conway.