Flanker Underhill has missed much of the past few months after suffering concussions and then a hip injury but has done enough in his limited outings for Bath to convince coach Eddie Jones that he is worth a place in the 36-man squad named on Sunday.
With his former England back-row partner Tom Curry working through the return to play protocols after he suffered a head injury in the win over Wales, Underhill could go straight into the starting team.
Alex Dombrandt, who played well in the victory over Wales and looked to have made himself first-choice for the No.8 position, is expected to return to training later this week after testing positive for COVID-19 and could still be in contention to play.
Nic Dolly and Alex Mitchell are also included, for the first time since the 2021 autumn series, as are uncapped backs Louis Lynagh — the 21-year-old son of Wallabies' great Michael Lynagh, Orlando Bailey, Ollie Hassell-Collins and Luke Northmore.
Sale No.9 Raffi Quirke suffered concussion playing against Exeter in the Premiership on Sunday and is unavailable for selection.
Lock Jonny Hill, who has been undertaking rehabilitation on a leg injury since he arrived into camp, has returned to his club Exeter for the remainder of the tournament.
Both teams go into the match with two wins and one defeat.
Extedned England squad for Ireland game:
Forwards: Alfie Barbeary, Jamie Blamire, Ollie Chessum, Tom Curry, Nic Dolly (Leicester Tigers, 1 cap), Charlie Ewels, Ellis Genge, Jamie George, Joe Heyes, Maro Itoje, Joe Launchbury, Courtney Lawes, Joe Marler, Bevan Rodd, Sam Simmonds, Kyle Sinckler, Will Stuart, Sam Underhill.
Backs: Orlando Bailey, Elliot Daly, George Ford, George Furbank, Ollie Hassell-Collins, Louis Lynagh, Max Malins, Joe Marchant, Alex Mitchell, Jack Nowell, Luke Northmore, Harry Randall, Henry Slade, Marcus Smith, Freddie Steward, Ben Youngs.
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