The designation puts a six-month moratorium on any sale of the land, which is owned by Coin Street Community Builders.
It also allows the community to bid for the site when the trust seeks a sublease, during which time opposition group Thames Central Open Spaces (TCOS) will raise funds in a bid to buy the site and block the lease.
A judicial review on 10-11 June was due to consider whether it was unlawful for Lambeth to grant planning permission for the bridge to be built without certainty that maintenance costs would be covered.
But last week TCOS campaigner Michael Balls withdrew that case after gaining a court order forcing the trust to produce a guarantee that annual costs would be covered for the next 125 years.
London mayor Boris Johnson produced that guarantee on 4 June, promising the Greater London Assembly (GLA) would underwrite all the maintenance costs, estimated at £2.8m per annum. At the time of going to press TCOS was seeking legal advice on challenging that decision in the High Court.
Last week the GLA also passed a motion calling for a full audit of the project's procurement process and asking the mayor to remove Transport for London funding from the project.
Assembly member Caroline Pidgeon, who proposed the motion, said many other sites need a bridge more. "It is folly to cut down more than 30 mature trees and reduce much valued open space on the South Bank," she said.
"£60m of public funding could be far better spent improving numerous parks and open spaces."
A representative of the Garden Bridge Trust said: "We are pleased that the judicial review between Lambeth Council and Michael Ball has been resolved. With £125m raised and our preferred contractors appointed, we continue to make good progress, with detailed plans being developed and construction planned to start in early 2016.
"We will continue to work with local authorities, the community and businesses to ensure that benefits are maximised in the local area. We are confident the decision to list land on the south bank as a community asset will not impact the timetable for the construction of the bridge and we are moving ahead.
He added: "The London Assembly holds the Mayor to account and has performed this role in scrutinising the Garden Bridge, and expressing its view on the project. However, the Assembly does not approve decisions made by the Mayor and we understand that he remains in full support of the bridge."