The Italian veteran named his squad at 1530 BST and confirmed that McClean had made the final 23 after a stellar second half of the season with his club. However, Wigan's McCarthy will miss the tournament after his father was diagnosed with cancer and informed the national coach who told him he is in his plans for the future.
There were few surprises in the final squad with Stephen Hunt being included despite a recent injury scare.
Trap told the assembled media: "We have a strong team with organisation and balance."
McClean's addition to the squad was hailed by Trapattoni who told reporters: "He has a good personality, he's young, he's strong, physically strong. He's improved, he's grown. I think he can give us energy. He scores goals, it's very important."
He added: "With three games, we need the players to fill in for Duff and McGeady, maybe in the second or third games. It will also help him for the future. He will be confident."
James McCarthy issued a statement, saying: "I have made the difficult decision to withdraw my name from selection for the Euro 2012 squad following the diagnosis of my father with cancer and on-going requirement for treatment. I have discussed this with the manager. He was very understanding and I thank him sincerely for that."
Giovanni Trapattoni told reporters that McCarthy had broken the news to him last week and said that the player had made the right decision.
"I prefer him to stay at home. Psychologically he's not ready," said the former 73-year old.
"In the future, he will be with us in the next campaign."
Ireland squad for friendlies against Bosnia-Herzegovina on May 26, Hungary on June 4 and Euro 2012:
|Shay Given||Aston Villa|
|Richard Dunne||Aston Villa|
|Paul McShane||Hull City|
|Sean St Ledger||Leicester City|
|Keith Andrews||West Bromwich Albion|
|Paul Green||Derby County|
|Aiden McGeady||Spartak Moscow|
|Glenn Whelan||Stoke City|
|Simon Cox||West Bromwich Albion|
|Robbie Keane||LA Galaxy|
|Shane Long||West Bromwich Albion|
|Jonathan Walters||Stoke City|