Cullen, who was a second half replacement in the bonus point victory over Benetton Treviso last weekend, partners Ben Marshall in the second row.
Ireland international Shane Jennings is back in the starting line-up after missing the Treviso match and features in the back row alongside Jordi Murphy and Dominic Ryan, who scored a hat-trick of tries against the Italian outfit.
In the back-line, Isaac Boss links up at half-back with Noel Reid, who is one of three current Academy players in the starting line-up.
Andrew Goodman continues in the centre alongside Eoin O'Malley, while Fionn Carr, who makes his 35th appearance for his home province, joins Andrew Conway and David Kearney in the back-three.
Ian Madigan and Fergus McFadden are named amongst the replacements after their release from Ireland camp after training on Friday.
There are now over 15,300 tickets sold for Saturday's game and tickets will be available at the ground on the night.
Tickets are also on sale online here and can be purchased from the Leinster Rugby Store (Donnybrook), Spar (Donnybrook) and Ticketmaster outlets nationwide.
LEINSTER (v Scarlets): David Kearney; Andrew Conway, Eoin O'Malley, Andrew Goodman, Fionn Carr; Noel Reid, Isaac Boss; Jack McGrath, Aaron Dundon, Michael Bent, Leo Cullen (capt), Ben Marshall, Dominic Ryan, Shane Jennings, Jordi Murphy.
Replacements: Tom Sexton, Jack O'Connell, Jamie Hagan, Mark Flanagan, Rhys Ruddock, John Cooney, Ian Madigan, Fergus McFadden.