The remaining internationals, including Italian World Cup lock Carlo Del Fava, all started Ulster's 32-8 loss to Llanelli last time out.
Coach Mark McCall is looking forward to seeing how tomorrow night goes for new signing Dewey. He said: "Rob had a very successful World Cup with Scotland and has continued to impress us all at training since he joined the squad a few weeks ago. He has fitted in very well and everyone is really looking forward to his debut."
Dewey will partner Trimble in the centre, a new combination which will see the Scottish and Irish internationals playing alongside each other for the first time, with McCall enthused by the pairing.
"They are both international players, individually they are both very strong and physical centres so it will great to see them play alongside each other and see what they can do."
With Paddy Wallace and vice-captain Isaac Boss holding down the half-back slots, David Humphreys and Paul Marshall have been selected as cover for them on the bench.
Ulster will start with a new-look second row partnership with Del Fava being joined by Ireland 'A' forward Ryan Caldwell, who is available again after a three-match ban.
McCall admitted: "This is one combination we haven't really had a chance to look at until now. Everyone has been very impressed with Carlo so far and Ryan started his season off really well but has been unavailable recently due to suspension, so it will be exciting to watch how that combination works tomorrow."
Lock-cum-flanker Matt McCullough was not available for selection due to a minor foot injury picked up at training last week.
Ahead of the all-ticket game, McCall added: "The local derbies are the games the players look forward to. Both sides are back to full strength and we are very much looking forward to the clash."
Tickets for the game are still available online from www.UlsterRugby.com and the Ulster Rugby ticket line (tel: 028 9049 3222 (Option 2)) or alternatively from over the Ravenhill counter.
Tickets can also be bought from various ticket outlet shops across the province, including: In Sport - Newtownards, SS Moore's - Belfast, Athletic Stores - Belfast, Eden Park - Belfast, Euro Sport - Lisburn, Shoe Fair Sports - Banbridge, Style N Sport - Ballymena, Vi-Sport - Belfast, David Gotto All Sports - Belfast, Overplay Sports - Carrickfergus, Douglas & Grahame Ltd - Belfast.
ULSTER (v Leinster): Bryn Cunningham; Tommy Bowe, Andrew Trimble, Rob Dewey, Mark McCrea; Paddy Wallace, Isaac Boss; Justin Fitzpatrick, Rory Best (capt), Bryan Young, Carlo Del Fava, Ryan Caldwell, Neil Best, Kieron Dawson, Stephen Ferris.
Replacements: Nigel Brady, Declan Fitzpatrick, Justin Harrison, Roger Wilson, Paul Marshall, David Humphreys, Mark Bartholomeusz.