The Les Kiss-coached Irish side, which includes 28 players in the touring party, will also face Canada in Toronto the following Saturday (June 15).
It has been a rapid rise for O'Mahony who has experience of captaining teams at schools, club, provincial and international level, including stints at the helm of a number of Ireland underage teams and both the Munster senior and 'A' sides.
He made his Ireland senior debut against Italy in the 2012 RBS 6 Nations and now has 14 caps to his name, including 10 starts.
His versatility has seen him line out in all three positions in the back row for Ireland, and he even spent time on the wing during their last game of the 2013 Championship against Italy.
His tender years make him the youngest Ireland captain since Brian O'Driscoll - also 23 back then - skippered the team to victory over Australia in November 2002.
O'Mahony will also be the first Cork native to captain Ireland since the recently retired Ronan O'Gara did so against England in March 2008.
Notably, O'Mahony takes on the senior captaincy for the summer tour just as fellow back rower and his successor as Ireland Under-20 captain in 2010, Rhys Ruddock, gears up to lead the Emerging Ireland squad in Georgia next month.
As well as O'Mahony's promotion to the captaincy role, the addition of Rory Best to the British & Irish Lions squad means that Leinster hooker Sean Cronin will step up from the Emerging Ireland panel for senior duty in North America.
The player taking Cronin's place in the Emerging Ireland squad is Ulster hooker Niall Annett, who has also captained the Ireland U-20s in the recent past.
IRELAND Squad (North American Tour - USA & Canada):
Isaac Boss (Terenure College/Leinster)
Darren Cave (Belfast Harlequins/Ulster)
Tom Court (Malone/Ulster)
Sean Cronin (St. Mary's College/Leinster)
Declan Fitzpatrick (Belfast Harlequins/Ulster)
Jamie Hagan (Old Belvedere/Leinster) *
Iain Henderson (Ballynahinch/Ulster)
Chris Henry (Malone/Ulster)
Robbie Henshaw (Buccaneers/Connacht) *
Paddy Jackson (Dungannon/Ulster)
Felix Jones (Shannon/Munster)
David Kilcoyne (UL Bohemians/Munster)
Ian Madigan (Blackrock College/Leinster)
Kieran Marmion (Galwegians/Connacht) *
Paul Marshall (Belfast Harlequins/Ulster)
Mike McCarthy (Buccaneers/Connacht)
Fergus McFadden (Old Belvedere/Leinster)
Kevin McLaughlin (St. Mary's College/Leinster)
Tommy O'Donnell (UL Bohemians/Munster) *
Stuart Olding (Belfast Harlequins/Ulster) *
Peter O'Mahony (Cork Constitution/Munster) (capt)
Mike Ross (Clontarf/Leinster)
Mike Sherry (Garryowen/Munster) *
EMERGING IRELAND Squad (Tblisi Cup, Georgia):
Michael Allen (Belfast Harlequins/Ulster) *
Niall Annett (Belfast Harlequins/Ulster) *
Michael Bent (Dublin University/Leinster)
Andrew Conway (Blackrock College/Leinster) *
John Cooney (Lansdowne/Leinster) *
David Foley (UL Bohemians/Munster) *
Eoin Griffin (Galwegians/Connacht) *
Cathal Marsh (Dublin University/Leinster) *
Michael Heaney (Belfast Harlequins/Ulster) *
Rob Herring (Ballynahinch/Ulster) *
David Kearney (Lansdowne/Leinster) *
Ian Keatley (Young Munster/Munster)
Richard Lutton (Belfast Harlequins/Ulster) *
Brendan Macken (Blackrock College/Leinster) *
Jack McGrath (St. Mary's College/Leinster) *
Eoin McKeon (Galwegians/Connacht) *
Martin Moore (Lansdowne/Leinster) *
Niall Morris (Leicester Tigers) *
Jordi Murphy (Lansdowne/Leinster) *
Ian Nagle (Cork Constitution/Munster) *
Robbie Diack (Malone/Ulster) *
Tiernan O'Halloran (Galwegians/Connacht) *
Rhys Ruddock (St. Mary's College/Leinster) (capt)
Dominic Ryan (Lansdowne/Leinster) *
John Ryan (Cork Constitution/Munster) *
Lewis Stevenson (Malone/Ulster) *
* Denotes uncapped player
A number of players were not considered due to injury, including:
Stephen Ferris, Eoin Reddan, Luke Fitzgerald, Gordon D'Arcy, Luke Marshall, David McSharry, Keith Earls and Stephen Archer
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