The scheme has detailed planning consent for a leisure quarter in the town centre with 75,000 sq ft of retail space anchored by a multi-screen Picturehouse cinema and 161 new homes.
Ealing Council chose Land Securities to develop the site two years ago.
Riccardo Mai, Head of Development Management at Land Securities, said: “Land Securities is proud of the work we have done to facilitate development of the Filmworks project and bring a cinema back to Ealing.
“We are delighted to have now secured an agreement with St George, a company with unquestionable track record of delivering major developments”
Michael Bryn-Jones, Managing Director of St George PLC said: “We are delighted to continue our investment in Ealing with the acquisition of Ealing Filmworks. It will complement the success of Dickens Yard delivering a much wanted cinema, fantastic new shops and restaurants in the heart of Ealing town centre, as well as high quality homes.”