Langley Court, set in the leafy suburbs of Beckenham, Kent, was first established by Wellcome more than 70 years ago as its chief research centre for the drugs company. When Glaxo bought Wellcome in 1995, the site was assessed as an unnecessary duplication of facilities in the combined group.
Glaxo Wellcome has said that John Laing will be the preferred purchaser of the site, with a bid believed to be near to pounds 50m.
It will be the end of a long-running headache for the pharmaceuticals company, which has spent almost two years attempting to find a solution to the disposal of Langley Court.
Initially, it had tried to sell the 107-acre site off, lock, stock and barrel to another multinational, but there were no takers.
It then looked for a partner to develop the site as a science park, but access would have been too poor.
The current solution follows a planning application submitted to Bromley Borough Council by Glaxo Wellcome.
The company is due to meet with the council in early September to thrash out final details of the planning ap- plication. Glaxo Wellcome believes its current proposal will see 1,400 jobs established on the site, to replace those lost by the closure of the old Wellcome facilities.
It wants to retain 30 acres to house its main biotechnology research centre for the UK, to sell off 37 acres for redevelopment as light office use, to keep 45 acres as open space, and to devote 26 acres to residential housing. John Laing is expected to build up-market executive homes on the land.
Stewart MacMillan, chief planner for the London Borough of Bromley, said the site was in a very attractive area and had a lot of potential.
"We were very concerned about its future, when it was disclosed it was to be closed down, as it brought a lot of employment and money into the local economy."
While the council has a slightly different ratio of land use planned, Mr MacMillan said he expected a compromise could be reached between the two sides.
A spokesman for Glaxo Wellcome said the company would gift the open space to the local community. Over the years, it has been well tended by Wellcome, with nature trails established and a lot of landscaping.
Some of the buildings on the site - including the main mansion block and an estate office that is known as the chapel - are listed.