Westfield bought a 50 per cent stake in the scheme from the billionaire Reuben brothers, and the remaining 25 per cent from developer Stanhope.
The move comes after the owner of the site, London & Continental Railways, threatened to fire the original joint venture which was riven by arguments over the control of the project.
Stratford City will host 17,000 athletes for the Olympic Games, with the accommodation to be sold later as housing.
The row over how to develop the retail element of the project erupted publicly in May when London Mayor Ken Livingstone accused the Reubens of delaying the scheme and told the Iraqi-born brothers to 'go back to Iran'.
LCR sent the warring parties a letter on April 28 threatening to find another developer unless they resolved their differences within 42 days.