The Dons Trust, owners of AFC Wimbledon, have exchanged contracts with Chelsea for the sale of their Kingsmeadow stadium.
Chelsea want to use the ground for their youth and ladies' teams.
The deal will not be finalised until a number of conditions have been met, which include the Dons obtaining final planning permission for a new home.
Their plans to develop the greyhound stadium in Plough Lane are being scrutinised by the Mayor of London.
The decision by the Mayor's office followed Merton Borough Council approving Wimbledon's application for the greyhound stadium site.
Funds raised by the sale of Kingsmeadow to Chelsea will help towards the cost of their proposed new ground, which will have a capacity of 20,000.
AFC Wimbledon won promotion to League One via the play-offs last month and chief executive Erik Samuelson described the deal as "a major milestone".
He continued: "The proceeds of this deal are an essential part of the financing of the new stadium.
"The vision of a return to Merton, with all the community benefits it also brings, is now becoming very real."
The Dons have played at Kingsmeadow, which is also home to non-league side Kingstonian, since their formation in 2002.
They bought the ground from the K's in 2003 and as part of the sale to Chelsea will make a "substantial donation" to Kingstonian, allowing the Ryman League club to secure their future at another ground in or around Kingston.