Hamilton teenager McCarthy was wanted by a string of English clubs
Hamilton midfielder James McCarthy has agreed a four-year contract to join Wigan Athletic for a fee of about £1.2m rising to £3m depending on appearances.
Wigan's English top-flight rivals Wolves also had an offer accepted by the Scottish Premier League club.
Accies chairman Ronnie MacDonald told BBC Scotland: "James is a superb prospect and I know Roberto Martinez and Wigan will look after him."
Wigan expect the deal for the 18-year-old to be concluded within 24 hours.
Promoted Wolves were the first club to agree a fee, but once Wigan joined the race it meant it would be down to the player to choose a preferred destination.
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
Hamilton Accies chairman Ronnie MacDonald
Tottenham Hotspur made a late expression of interest, while Celtic manager Tony Mowbray admitted that his club were being priced out of the race after they, Burnley and Portsmouth had bids rejected earlier this summer.
And it appears to have been manager Martinez's promise of involvement in the first-team squad that tipped the balance in favour of Wigan.
McCarthy, who rejected a transfer to Liverpool in 2007 and was also linked with Chelsea, received no such guarantees from Premier League rivals Spurs or Wolves.
He told Accies' website: "I had an absolutely brilliant time at Accies. The club have been tremendous with me."
The Republic of Ireland Under-21 international travelled to Wigan on Monday and will join his new team-mates at their pre-season training camp in Austria.
He follows former Hamilton team-mate Brian Easton to the Barclays Premier League after the Scotland Under-21 left-back moved to Burnley for £350,000 last week.
Now Accies have trebled their previous record sale - they received £380,000 from Millwall for Paul Hartley in 1996 - for McCarthy.
"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."
MacDonald, who thinks the Scottish FA missed out on a great talent, was recalling the decision by Glasgow-born McCarthy to accept an offer to become part of the Republic of Ireland set-up after they were first to approach the teenager.
There is a possibility that a third product of the Hamilton youth system, James McArthur, could also be on his way to England's top flight.
His agent, Willie McKay, who also acts for Easton and McCarthy, claims Premier League clubs are interested in signing the 21-year-old midfielder, although there have been no firm offers yet.
Wigan, who had already signed Honduras midfielder Hendry Thomas and midfielder Jordi Gomez, on Saturday signed former St Johnstone striker Jason Scotland from Swansea for £2m.
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