The Athlone native, who is in his third year of the Connacht Academy, has captained Connacht Eagles in the British & Irish Cup this season and has featured from the bench in PRO12 games against Benetton Treviso and Munster.
Carty's first of three senior caps came against Glasgow Warriors at Scotstoun Stadium in September 2012.
Saturday night sees 21-year-old scrum half Kieran Marmion, who is Connacht's top try scorer so far this season, play his 44th consecutive game since his debut in 2012.
Darragh Leader has also been brought up from the Academy and starts at full-back in place of the injured Gavin Duffy. The 20-year-old Galway man has played in three games this season, starting two on the wing at home against Glasgow Warriors and the Scarlets.
The pack remains unchanged from last weekend's defeat to Munster with talented flanker Andrew Browne earning his 100th cap for the province.
John Muldoon is once again named at openside flanker, while Jake Heenan remains on the injury list. Craig Clarke will captain the side from the second row.
Previewing the game, Pat Lam said: "With our second and third choice out-half out injured, we have decided to bring in young Jack Carty to start.
"Jack has been involved with us in training all year and has had some good performances with the Eagles. It is a great boost to his development as a young Irish-qualified 10 to play against such quality opposition and I know he is very much looking forward to the test.
"Young Darragh (Leader) will start at full-back, a position in which he has proven himself with the Ireland Under-20s in the Junior World Championship last summer.
"We have an extremely young back-line going up against the best team in Europe and the league champions.
"But we have a belief in our young squad and if every player does their job and commits to the game-plan we've put in place, then we have every chance of getting the desired result."
CONNACHT (v Leinster): Darragh Leader; Fionn Carr, Robbie Henshaw, Eoin Griffin, Matt Healy; Jack Carty, Kieran Marmion; Brett Wilkinson, Jason Harris-Wright, Nathan White, Michael Kearney, Craig Clarke (capt), Andrew Browne, John Muldoon, Eoin McKeon.
Replacements: Dave Heffernan, Denis Buckley, Rodney Ah You, Michael Swift, George Naoupu, Paul O'Donohoe, Dan Parks, Tiernan O'Halloran.