The 21-year-old replaces club colleague Andrew Trimble in the only change to the side that lost to South Africa a fortnight ago having crossed for a hat trick of tries in the 53-0 thrashing of the Fijians at Thomond Park.
Gilroy, who signed a new contract extension at Ravenhill earlier this week, starts alongside 2009 Test Lion Tommy Bowe and Munster youngster Simon Zebo in the back three, with Zebo retained in his less customary position of full back.
"Craig was someone we had invested a lot in for the future but, on the back of his performance last week, perhaps that future isn't too far off," said Kidney at this afternoon's team announcement.
"He's managed things that have come his way well so far and the way he's carried himself off the field has impressed me."
Jamie Heaslip continues to captain the side in the absence of fellow Lions Brian O'Driscoll and Paul O'Connell, while Jonathan Sexton is again preferred to triple Lions tourist Ronan O'Gara at outside-half.
Ireland are still without Lions contenders Stephen Ferris, Sean O'Brien, Rory Best and Rob Kearney through injury but 2005 and 2009 Lion Donncha O'Callaghan could win his 90th Irish cap from the bench.
Saturday's winners will secure a place in the top eight of the IRB rankings and therefore claim a spot among the second seeds for the 2015 World Cup draw.
But the losers will slip into the third tier of seeds for December's draw and will then be forced to face the possibility of being selected in a pool containing two major nations.
Ireland (v Argentina, Aviva Stadium, Saturday, 2pm)
Simon Zebo (Munster); Tommy Bowe (Ulster), Keith Earls (Munster), Gordon D'Arcy (Leinster), Craig Gilroy (Ulster), Jonathan Sexton (Leinster), Conor Murray (Munster); Cian Healy (Leinster), Richardt Strauss (Leinster), Mike Ross (Leinster), Donnacha Ryan (Munster), Mike McCarthy (Connacht), Peter O'Mahony (Munster), Chris Henry (Ulster), Jamie Heaslip (Leinster, capt)
Replacements: David Kilcoyne (Munster), Sean Cronin (Leinster), Michael Bent (Leinster), Donncha O'Callaghan (Munster), Iain Henderson (Ulster), Eoin Reddan (Leinster), Ronan O'Gara (Munster), Fergus McFadden (Leinster)