The plan is to nearly triple the size of the existing shopping centre, taking it from 44,000 sq m to 120,000 sq m.
The extra retail element is expected to include two department stores, a supermarket, shop units, financial and professional services and a food court.
To help improve transport links, a new transport interchange is to be built consisting of a new bus station, tram stop and multi-storey car parks.
The centre is owned in a joint venture between Westfield and the Royal Mail Pension Fund.
Peter Miller, chief operating officer at Westfield, said: “This decision means we are now able to draw up detailed plans for the development and provides an extra layer of confidence which will enable us to take our discussions with potential retailers to the next stage.
“We understand the importance of this project as a major catalyst for the regeneration of the south of the city and we look forward to progressing the major project as quickly as possible with preparation works for the first phase already underway”