Irish investor Ballymore has acquired a "substantial stake" from Merepark to become the new joint venture partner in Inacity's 60-storey Eastgate Tower scheme in Manchester's Piccadilly.
Inacity and Ballymore will start on site in January, after a wait of more than two years since plans were approved.
The move is Ballymore's first into Manchester and brings Sean Mulryan, head of Ballymore, into the same patch as his brother Donal, who runs West Properties and is a major player in the city.
Wayne Mellor, chief executive of Inacity, declined to confirm speculation Ballymore had paid £30m for the stake in the 620ft tower scheme.
Merepark, based in Cheshire, is working with Ballymore on the development of the £160m Central Village retail-led scheme in Liverpool.
Inacity was granted planning consent in 2005 for 700 flats, a 220-bedroom hotel and more than 30,000 sq ft of commercial space in a 60-storey tower.
If built, the tower would be taller than Manchester's 554ft Beetham Tower and be the tallest residential tower in the UK.
Car park operator NCP has been served notice to vacate the Ducie Street site by the end of 2007, but will return to operate a 400-space car park when the building is completed.