The move comes after a campaign by Islington Play Association, which has been trying to secure protection for land on which children play.
The legal covenant, called a deed of dedication, will mean that no adventure playground in the authority can be sold or built on.
Anita Grant, director of Islington Play Association, said: “We have been campaigning for this protection for more than two years.
“We have had loads of support from parents, the council, people working in the borough, the community and also from the City Bridge Trust because everyone recognises the importance of excellent play opportunities for the children of Islington.
“This is a great step for play in Islington and a model for the rest of the country too.”
The council has also pledged a budget of £1.24m for its adventure playgrounds. Both measures were implemented following a review of playgrounds in the authority and how they benefit children and young people.
Six of the playgrounds in Islington are currently run by the voluntary sector and the report proposes that these be brought under the management of one organisation for an initial period of two years from April 2013 to enable a more consistent approach to managing the playgrounds.
Councillor Richard Watts, Islington’s executive member for children and young people, said: "We are committed to ensuring that Islington's adventure playgrounds remain open and free for all young people in the borough. This plan means that we can safeguard adventure play in Islington while also making sure that the playgrounds are run effectively, providing high-quality services and value for money.
"In Islington we have the second lowest level of open space per head nationally. While other boroughs have taken the decision to charge for adventure playgrounds, we're absolutely determined not to do this. We want the borough to be a fairer place where all young people can have access to safe spaces outdoors where they can play."
In 2015, Islington Council will consider whether to retender the contract for six of its playgrounds, or whether to take over their management.