The 19 and 13 storey tower block scheme of 366 luxury flats was granted planning in March 2020 but both the council and developer had been wrangling over section 106 requirements.
Under the deal, De Trafford will pay an initial £330,000 towards off-site affordable housing for the first phase of the development.
It was agreed after a viability assessment prepared by Eric Wright Construction and consultant Gleeds provided with a forensic breakdown of how much money it will take to deliver Gallery Gardens.
Construction costs were estimated at just over £62m for the first phase.
The project will be located in Castlefield between Hulme Hall Road and Ellesmere Street.