Gilroy replaces Ulster colleague Andrew Trimble, who drops out of the 23 altogether, in the only change to the side beaten 16-12 by South Africa two weeks ago.
Coach Declan Kidney has rewarded the uncapped 21-year-old for his dynamic display in Saturday's non-cap international against Fiji.
Gilroy scored three tries in the 53-0 victory at Thomond Park and has profited from Trimble's disappointing afternoon against the Springboks.
The clash with Argentina has taken on critical significance, prompting Kidney to revert to the XV that opened the autumn schedule, apart from Gilroy.
Saturday's winners will secure a place in the top eight of the IRB rankings, which are being used to determine the seedings for the 2015 World Cup.
The losers will slip into the third tier of seeds for next month's draw and face the possibility of being selected in a pool containing two major nations.
Adding further impetus to Ireland's quest for victory is their current five-Test losing sequence, their worst run for 14 years.
If Argentina add to their misery at Lansdowne Road, Kidney's position will come under intense scrutiny.
Ireland are missing highly-influential Brian O'Driscoll, Paul O'Connell, Rory Best, Stephen Ferris, Sean O'Brien and Rob Kearney to injury, but the South Africa game was a missed opportunity to claim a prized southern hemisphere scalp.
The rivals have met on 12 previous occasions with the Irish winning seven matches, including the last two.
S Zebo (Munster); T Bowe (Ulster), K Earls (Munster), G D'Arcy (Leinster), C Gilroy (Ulster); J Sexton (Leinster), C Murray (Munster); C Healy (Leinster), R Strauss (Leinster), M Ross (Leinster), D Ryan (Munster), M McCarthy (Connacht), P O'Mahony (Munster), C Henry (Ulster), J Heaslip (Leinster, capt).
Replacements: S Cronin (Leinster), D Kilcoyne (Munster), M Bent (Leinster), D O'Callaghan (Munster), I Henderson (Ulster), E Reddan (Leinster), R O'Gara (Munster), F McFadden (Leinster).
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