The 24-acre revamp will see the firm now press ahead with building a new Market Hall, 120-bed Hampton by Hilton hotel, 56 flats, eight townhouses and over 4,000 sq ft of retail space.
Demolition and enabling works have been under way this year.
The reserved matters green light from St Helens Borough Council allows building to start on the redevelopment of the former Hardshaw Centre into a revitalised central district
Council leader Anthony Burns said the scheme was a “defining moment for St Helens” that would boost jobs, skills and quality of life.
Matt Whiteley, senior project manager at ECF, said sustainability was central to the design with low-carbon timber structures and green infrastructure that brings nature back into the centre of town.
Phase One is expected to generate 485 new jobs and £23.2m a year in GVA, supported by a £69.2m council funding package and Government contributions via the Town Deal and Brownfield Land Release Fund.
The plans are closely tied to the new St Helens Transport Interchange, which was approved in July and will create a modern gateway into the borough.