Brook, 24, has been called up as batting cover for the four-match series, starting in Cardiff on Friday.
Jonny Bairstow has a shoulder issue and fellow batter Dawid Malan's wife is due to give birth in the coming weeks.
Brook has also been named in a squad captained by Zak Crawley for three matches against Ireland that follow.
England's World Cup party will all sit out the Ireland series, which ends 26 September - nine days before England's World Cup opener against New Zealand on 5 October.
Warwickshire batter Sam Hain, Surrey wicketkeeper-batter Jamie Smith and Derbyshire bowler George Scrimshaw are in line for their first caps.
Brook was a surprising omission when England named their one-day international squad to play New Zealand last month, which also doubled as their provisional World Cup squad.
But the Yorkshire batter followed that with a century in The Hundred, plus 48 not out and 67 in the first two matches of the T20 series against New Zealand that concluded on Tuesday.
England have until 28 September to submit their final 15-strong World Cup squad.
England squad to play Ireland: Zak Crawley (Kent, captain), Rehan Ahmed (Leicestershire), Harry Brook (Yorkshire), Brydon Carse (Durham), Ben Duckett (Nottinghamshire, vice-captain), Sam Hain (Warwickshire), Will Jacks (Surrey), Craig Overton (Somerset), Matthew Potts (Durham), Phil Salt (Lancashire), George Scrimshaw (Derbyshire), Jamie Smith (Surrey), Luke Wood (Lancashire)
Bairstow scored 73 from 41 balls against New Zealand in the fourth T20 on Tuesday but then did not keep wicket as planned because of pain in his right shoulder.
He has since been assessed and the issue is not thought to be serious, England instead being cautious with the start of their World Cup defence less than a month away.
Brook's call-up puts him in line to go to India as one of three travelling reserves at worst, but a strong performance against New Zealand could mean he forces his way into the full squad.
On Tuesday, coach Matthew Mott said the door was still open to Brook.
"The guys that are in that 15 have got the first crack at it but as we've said throughout, we'll just monitor and see how players are going and make some fine-tuning if needs be," he told BBC Sport.
Crawley, who has played 39 Tests but only three ODIs - all in a series against Pakistan in 2021 when an entirely new squad was named because of a Covid-19 outbreak, will captain England for the first time against Ireland, with his Test opening partner Ben Duckett his deputy.
Surrey's Jamie Overton and Essex's Sam Cook were left out because the series clashes with the latter stages of the County Championship, with Surrey and Essex currently first and second in Division One.