The pair join Kaden Rodney, Jack Wells-Morrison and Joe Whitworth as international call-ups after the trio were named in England's Under-18s squad.
Adaramola is named for the first time at Under-21 level. The Dublin-born 18-year-old has been selected for the Under-19s before, and joins more seasoned U21 international O'Brien for three games in June.
O'Brien spent the second half of 2021/22 on loan with League Two Swindon Town, where he made 21 appearances.
Should the Ireland side succeed in their qualifiers, they will become the country's first Under-21s team to reach the European Championship finals.
Ireland U21 fixtures
All times are BST
- Friday, June 3rd: Ireland v Bosnia & Herzegovina (19:30)
- Monday, June 6th: Ireland v Montenegro (17:00)
- Tuesday, June 14th: Italy v Ireland (16:30)
You can find out how the lads fare by staying tuned to cpfc.co.uk, the official app and our social media channels.