Curtis Tilt leaves Rotherham United
The centre-half has had three loans spells with the Millers' League One promotion rivals during a difficult two-year spell at AESSEAL New York Stadium and has now moved to the Latics permanently.
The deal was agreed between the two clubs at the weekend and Rotherham will get a return on the £100,000 they paid to take Tilt from Blackpool in January 2020.
Tilt endured a frustrating time in South Yorkshire and the 30-year-old made only one appearance for the Millers.
He has long been keen on a full switch to the DW Stadium.
Wigan, who are in top spot, made several bids before reaching a figure that Rotherham owner Tony Stewart found acceptable.
When asked if Tilt's departure could free up money for potential signings, Millers manager Paul Warne said: "Possibly."
The transfer window closes at 11pm on Monday and the boss hasn't ruled out at least one incoming.
"The recruitment team are trying to help us," he said. "We need some fresh blood but new arrivals have to be affordable and, obviously, available."