The site has been an eyesore in the city since previous developer Windsor went bust in 2007, halfway through the concrete package, leaving Laing O’Rourke nursing big losses.
Balfour Beatty will now start work by the end of the summer on the first of two residential blocks. The third building is earmarked for an hotel and fourth for leisure or offices.
Neptune is in joint venture with Barclays, which is owed £25.5m as the main creditor to Windsor’s scheme.
Neptune Developments’ managing director, Steve Parry, said: “This is an exciting scheme for us – one which will radically enhance this particular site with four new buildings and the improved public realm.
“We are aiming to make a hugely positive contribution to the overall regeneration of the city centre.”
The Neptune scheme has been designed by Liverpool architects Falconer Chester Hall.