Martinez had pin pointed the youngster as one of his primary targets right from the moment he took over for Steve Bruce, who moved to Sunderland. With a large hole left in central midfield following Wilson Palacios' move to Tottenham Hotspur, the new Latics manager moved quickly to bring in one of the most sought after young talents in Britain.
There were many teams expected to come in for McCarthy, but only Wolves and Wigan contacted the Accies about the youngster.
After James had traveled down south to meet his prospective managers, and the clubs had agreed upon the fee, clubs like Spurs and Portsmouth expressed their interest, while teams like Liverpool, Chelsea, and Deportivo La Coruna, who had all showed major interest in the past, sat waiting in the wings.
But any interest they had, if any, was extinguished after McCarthy, who had been swayed by the charasmatic Spaniard, Martinez, agreed to join Wigan.
The major reason for the 18-year-old choosing to join Wigan over some of the Premiership's more illustrious clubs is that Martinez has promised him that he will be involved with the first team this season.
Roberto Martinez stock has risen over the last couple of seasons. After making his debut in management with Swansea in 2007, the Spaniard took to the job like a duck to water and recorded his first manager of the month award only two months into the job.
To further increase his growing reputation, Martinez guided Swansea to the League One title in his debut season, scooping the League Managers Award for Manager of the Year into the bargain.
With Martinez highly regarded in the game, especially as Swansea were one of the best footballing teams in Britain, Alex Ferguson offered him the Assistant Managers role at Old Trafford only for Martinez to opt to stay with The Swans as they strove for Premiership promotion.
During his short time as a manager, Martinez has won many admirers for the way in which he has imposed his footballing philosophy onto a team with meager resources, making a mockery of some managers stances for playing "agricultural football" because they have so few resources.
McCarthy is one of the most highly regarded young players in Britain, and has courted his own fair share of controversy in his short career since making his debut at 15.
After many of Europe's top clubs scouted the youngster, Liverpool offered £1 million for the then 16 year old. But McCarthy and his manager Billy Reid decided that the best place for him to progress as a youngster was with the Accies, so the bid was turned down.
Clubs as far a Spain and Germany came to scout the youngster whose reputation was growing with every appearance, but the Scottish FA showed great reluctance to call up the youngster from the Irish enclave of Castlemilk.
The deep rooted sectarian history in Scotland seemingly showing it's head in the unlikeliest of places.
With Scotland waiting in the periphery, Ireland moved in as quickly as they could, and the rest is history.
McCarthy has gone on to represent Ireland at every level, as well as winning the Scottish Young Player of the Year award in 2009, and is now expected to earn his first cap for Giovani Trappatoni in the upcoming friendly against Australia in Thomand Park, and he may well force himself into Ireland's World Cup squad.
Accies chairman Ronnie MacDonald told BBC Scotland: "James is a superb prospect and I know Roberto Martinez and Wigan will look after him."
"We are very sad to see them go, but that is what Hamilton Accies are about—taking young boys through our youth system and giving them a chance," said MacDonald.
"They have become very wealthy young men and I am delighted for them."
"It's a disgrace that James was not capped for Scotland."
McCarthy joins Wigan's other recent signings, Jason Scotland, Honduras midfielder Hendry Thomas, and Jordi Gomez.
Roberto Martinez has plenty of work to do at Wigan, they slipped backwards in the Premiership in the last six months and if he is to re-establish them as a fixture in the EPL, he'll have to bring the best from his recent signings, the potential is definitely there, for manager, club, and James McCarthy.
Roll on August 15.
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