The big centre-back was recalled from a season-long loan by the Millers midway through this month.
After more than a week of negotiations, the two clubs have finally reached agreement on a six-figure sum which will see him join Latics on a full-time basis.
It's understood to be in the region of the £100,000 Rotherham paid Blackpool two years ago.
"I cannot see it breaking down, I would expect it to go through," said Rotherham boss Paul Warne - the ex-Latics striker - after Saturday's 1-0 home win over Cheltenham.
Latics chairman Talal Al Hammad hinted the deal was imminent on Friday night when he tweeted his trademark pen along with the flag of Jamaica - the country Tilt represents at international level.