The 22-year-old midfielder finally met up with his international colleagues on Tuesday morning after being given permission by manager Giovanni Trapattoni to stay behind to tie up his move to Goodison Park.
And McCarthy received a particularly warm welcome from Merseyside-born Stoke striker Walters.
"He was delighted to get the move," said Walters. "I'm an Everton fan as well, so I am delighted for him.
"He's going to a great club and he's got friends there with Seamus (Coleman) as well, going to a manager he knows and who trusts him, so it's a great move for him."
It proved an eventful end to the transfer window for another member of the Ireland squad, with Shane Long dashing back across the Irish Sea but failing to tie up a move to Hull, much to the disappointment of potential new club-mates Paul McShane and Robbie Brady.
However, Walters is confident the collapse of Long's proposed transfer will not distract him from his preparations for Friday night's World Cup qualifier against Sweden.
He said: "I think a lot of West Brom fans would have been unhappy if he had gone.
"The Hull lads are a bit gutted they didn't get him, but he's at West Brom and he's had a really good couple of years there and I don't expect any different from him next year."
With the transfer window now closed, Walters, McCarthy, Long and the remaining members of Giovanni Trapattoni's squad have turned their attention towards a key double-header against the Swedes and Austria which is likely to determine the destiny of their qualifying hopes.
The three teams are currently level in joint-second place on 11 points behind Group C leaders Germany, and defeat in either game could prove disastrous.
But the memories of a disappointing Euro 2012 finals campaign, which saw Ireland fail to claim a single point from their three group matches, is fueling their efforts to win a swift return to the big stage.
Walters said: "After the disappointment of the Euros, being there and being so disappointed to go out like we did, you want to get straight back into it.
"Once you have a taste of it, you want to get back in, so everyone is determined to get to Brazil.
"We are all really hungry for these two games and they are going to define where we are going to end up in the group, so they are exciting games to play in.
"You go into every game trying to win. Obviously, the emphasis is on us because we are at home in the first game against Sweden.
"But after that result, whatever it may be, you take each game as it comes, so we will see where we stand after that game and going into the last few games.
"It would be nice to get two wins, and that's what we will probably be aiming for, but we will see where we are after the game."
Trapattoni has on more than one occasion fielded Walters in a wide midfield position and it is a role he could be asked to fill once again on Friday night with Aiden McGeady missing through injury.
The 29-year-old freely admits he would prefer a more orthodox mission, but is happy to answer his manager's call whenever it comes.
He said: "I have always said I prefer to play up front as a striker, but in the past few years I have played as a wider man, whether it be right or left.
"But wherever you are called upon, you do your best and in the past few years, I have bee okay playing out there, so it's nothing new to me."