The Celtic and Scotland defender seemed set to sign for Middlesbrough after spending 48 hours holed up in a hotel on Teesside.
Caldwell even passed a medical with the Coca-Cola Championship club as Strachan's bid to revive Boro's fortunes saw him close in on a quartet of deals, including Barry Robson, Chris Killen and Willo Flood.
But, in a dramatic U-turn, Caldwell accepted an improved offer from Wigan that will earn him in excess of £20,000-per-week plus appearance money over the course of a four-and-a-half year contract.
Bumper deal: Caldwell will join Wigan
Despite desperate last-ditch efforts by Boro to change his mind last night, a senior Wigan source told Sportsmail they expect to seal the deal first thing this morning.
Roberto Martinez also moved to secure Ivory Coast international defender Steve Gohouri yesterday, with 27-year-old Caldwell next in the door.
'We knew the lad was keen to work again with Gordon Strachan at Middlesbrough but we wanted him to come here and made him a very good offer,' said Wigan chairman Dave Whelan.
'You always think a player will fancy a crack at the English Premier League rather than the Coca-Cola Championship.'
Celtic will land around £1m for a player with just over five months left on his contract, a similar trick to the one chief executive Peter Lawwell pulled off when Shaun Maloney joined Aston Villa in January 2007.
It also justifies Caldwell's stubborn stance on his own worth which led to an 18-month impasse between club and player over a new contract.
Big future: Bougherra sees himself moving away from Ibrox
As Sportsmail revealed last Wednesday, it was an aborted move for Rangers defender Madjid Bougherra that led to Wigan boss Roberto Martinez turning his attention to Caldwell.
Bougherra is understood to have said he sees his future at a bigger club after he leaves Ibrox.
'Roberto Martinez definitely had an interest in Madjid Bougherra,' confirmed Whelan.
Meanwhile, New Zealand international Killen is seeking assurances from Strachan as he aims to safeguard his World Cup Finals place.
The 28-year-old asked his former Parkhead boss Strachan why he was moving for him when, during two years together in Glasgow, he rarely pulled on a Celtic shirt.
With 10 goals for his country in 29 appearances, Killen needs games ahead of this summer's showpiece in South Africa.
'Chris has spoken to Gordon about his chances of getting a game,' said Killen's agent, Frank Trimboli.
'Obviously, there were spells a Celtic when he spent a lot of time on the bench or the sidelines.
'This is a massive year for him with New Zealand at the World Cup for the first time since 1982. He's hoping he can go to Middlesbrough, make the team and startscoring goals there before the Finals.
'Gordon does not have a lot of firepower currently. Any decent Championship club needs four main strikers and, at the minute, he only really has Leroy Lita and teenagers from the youth academy who are not yet ready to step up.'
Paul Caddis is another Celtic player heading for the exit door as manager Tony Mowbray's revolution gathers pace.
The reserve right-back has been lined up to join Swindon Town on loan until the end of the season.
The League Two club already have Simon Ferry and Ben Hutchinson on short-term deals and signed Scott Cuthbert from Celtic last summer.
Boss Danny Wilson said: 'Paul is one that we know about and we are hoping to bring him in.
'We know where his assets are and what his best positions are and that is anywhere down the right-hand side.'
The Scotland Under-21 international had a loan spell at Dundee United last season.
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