The 23-year-old was eventually reunited with former manager Roberto Martinez at Goodison Park but it was only in the earlier hours of the morning the deal was confirmed.
McCarthy endured a turbulent end to the previous season, starring in Wigan's FA Cup final triumph over Manchester City before the club was relegated to the Championship.
Former Wigan boss Martinez was recruited by Everton in the summer as David Moyes left to succeed Sir Alex Ferguson at Manchester United and McCarthy was one player he was eager to take with him.
Transfer deadline day arrived and with a deal yet to be sealed, McCarthy made a late night drive down the M58 to finalise a switch back to the top flight.
"I'd just been pacing up and down the living room," he told the Independent.
"I was just there, at home, just wondering if it was going to happen. Then I was told to drive up and, hopefully, something would get sorted out in time.
"It was eight minutes to 11. At that stage, I know it was all secure. After getting it all signed, there was no else there. It was the middle of the night.
"It was the high point of the year - no doubt about it. It's been a year of ups and downs, highs and lows, but nothing tops signing for a club like Everton."
Although the Republic of Ireland international eventually sealed a deal to return to the Premier League, the 2013/14 season began with a visit to Oakwell to face Barnsley and McCarthy admits the Championship poses a very different test for players.
"It's a really tough league, really end-to-end stuff," he added.
"It was difficult - wondering if [the move] was going to happen, with people."
Although Wigan's league campaign was suffering at the time, McCarthy was delighted to have experienced Wembley elation as Ben Watson's last-gasp header clinched victory over Manchester City; but the central midfielder believes Martinez deserves plenty of the plaudits.
"The Cup final was incredible," he said. "We went to the game thinking, 'we can cause an upset', when a lot of teams would freeze.
"The manager was a tactical genius on the day; I think he's got something different that a lot of managers don't have."
Martinez brought McCarthy to England from Scottish side Hamilton Academical and the playmaker praised the Spaniard for playing such a prominent role in his development.
"I had to wait six months at Wigan to get used to the systems and the English game," he explained.
"It was the same at Everton, where I had to wait a few weeks to get my place in the first team. But Martinez has always believed in me.
"He gives you the confidence to believe you can do things. He doesn't always feel the need to scream.
"Now and again if he needs to tell you something he will get it across and you can definitely hear him on the side of the pitch. But he finds other ways to get his point across, too."