Diack played for Emerging Ireland in last summer's Tbilisi Cup and lined out for the O2 Ireland Wolfhounds against England Saxons in January.
There are two further uncapped players on the bench as Connacht duo Kieran Marmion and Rodney Ah You hope to claim their first caps.
The front row sees Jack McGrath win his ninth cap - and second start - alongside hooker Rory Best and Mike Ross.
Captain Paul O'Connell is partnered in the second row by the 22-year-old Iain Henderson, who is the youngest member of the matchday squad alongside Marmion (also 22).
It will be O'Connell's 100th Test match - 93 appearances for Ireland and seven with the British & Irish Lions. He is the fourth Irishman to play in 100 international games after Brian O'Driscoll (141), Ronan O'Gara (130) and John Hayes (107).
The back row is made up of Ulster team-mates Diack and Chris Henry with Leinster's Jordi Murphy, who is making his first start at this level, wearing the number 8 jersey.
Conor Murray and Jonathan Sexton start at half-back with Luke Marshall and Darren Cave in the centre.
Marshall and Cave are two of the seven Ulstermen in the selected team - their biggest representation in an Irish side since the 2007 Rugby World Cup warm-up game against Scotland.
The back-three is made up of wingers Simon Zebo and Andrew Trimble and Munster's Felix Jones at full-back. Zebo and Jones are picking up their first caps since last year's summer tour.
Commenting on the team selection, Joe Schmidt said: "It was difficult in some ways but it was actually relatively easy in other ways. There are a number of players that are fatigued from the PRO12 final, there are a number of players that we wanted to give an opportunity. We have this one window to really do that.
"The GUINNESS Series is going to be immeasurably tougher with South Africa and Australia, but it's going to be very, very tough here, and one of the things that you want to find out is how the players cope in a tough environment.
"It will be hostile (on Saturday), it's a place where Test match rugby hasn't been before so the local population will be very much behind the Argentinians."
Looking forward to seeing how the new combinations fare this weekend, he added: "If the opportunity is afforded to you then I think you've got to reciprocate with the best performance you can put together.
"The way the players have trained this week that's certainly what they are working towards with the combinations we have, with the combative nature of the way the Argentinians play.
"They are a little bit unknown, they are a little bit harder to predict than other teams we have played. Then to be able to react and endure what will be a pretty tough Test match in a very tough environment, it's going to give us a bit more information about how these guys will cope in the future."
Saturday's first Test will be broadcast live on Sky Sports 1 HD (coverage begins at 7.30pm). The teams will play for the Admiral William Brown Cup which is named in memory of the Irish-Argentine Navy admiral William Brown.
IRELAND Team & Replacements (v Argentina, Estadio Centenario, Resistencia, Chaco, Summer Tour, Saturday, June 7, kick-off 3.40pm local time/7.40pm Irish time):
15. Felix Jones (Shannon/Munster) 5
14. Andrew Trimble (Ballymena/Ulster) 55
13. Darren Cave (Belfast Harlequins/Ulster) 5
12. Luke Marshall (Ballynahinch/Ulster) 5
11. Simon Zebo (Cork Constitution/Munster) 6
10. Jonathan Sexton (Racing Metro 92) 43
9. Conor Murray (Garryowen/Munster) 27
1. Jack McGrath (St. Mary's College/Leinster) 8
2. Rory Best (Banbridge/Ulster) 75
3. Mike Ross (Clontarf/Leinster) 39
4. Iain Henderson (Ballynahinch/Ulster) 10
5. Paul O'Connell (Young Munster/Munster) 92 (capt)
6. Robbie Diack (Malone/Ulster) *
7. Chris Henry (Malone/Ulster) 14
8. Jordi Murphy (Lansdowne/Leinster) 2
16. Damien Varley (Garryowen/Munster) 2
17. Dave Kilcoyne (UL Bohemians/Munster) 8
18. Rodney Ah You (Buccaneers/Connacht) *
19. Devin Toner (Lansdowne/Leinster) 15
20. Jamie Heaslip (Dublin University/Leinster) 65
21. Kieran Marmion (Corinthians/Connacht) *
22. Ian Madigan (Blackrock College/Leinster) 8
23. Fergus McFadden (Old Belvedere/Leinster) 26
* Denotes uncapped player