James McNabney, 23, has been selected for his first time with the Republic of Ireland side following a recovery from an anterior cruciate ligament injury that kept him out during the summer months.
McNabney previously represented the country in training squads before returning to competitive action this season.
Jamie Benson joins the squad after moving from Harlequins to Ulster in the off-season, bringing Irish eligibility through his mother who was born in Belfast.
Benson has not featured for Ireland previously but is now included in the selection alongside McNabney.
In the absence of captain Caelan Doris due to injury, Dan Sheehan will take charge as team leader for the upcoming fixtures.
Sheehan, currently playing for Leinster, is a former England Under-20 international and has been identified as the new skipper.
Ireland travel to the Aviva Stadium on Friday, 6 November to face Argentina in their first Nations Championship match of the campaign.
The Republic of Ireland will then host Fiji at the same venue on 14 November before departing for South Africa later in the month.
Earlier this year, Ireland secured victories against Australia and Japan but were defeated by New Zealand in the third summer Test.
The team's 2026 campaign saw them win the Triple Crown while failing to claim the Six Nations title after losing to France.
The current squad includes Bundee Aki, Rob Baloucoune, Jamie Benson, Craig Casey, Nathan Doak, Ciaran Frawley, Jamison Gibson-Park, Mack Hansen, Robbie Henshaw, Hugo Keenan, Stuart McCloskey, Jimmy O'Brien, Tommy O'Brien, Jamie Osborne, Sam Prendergast, Garry Ringrose and Jacob Stockdale.
Andrew Porter, Ryan Baird, Mack Hansen and Tommy O'Brien are returning to the group after missing the summer's fixtures due to injury.
Head coach Andy Farrell has managed a significant number of sidelined players this season, with Jack Crowley also excluded through injury alongside Boyle, Byrne, Conan, Henderson, McCarthy, Nash and Ward.