The US Justice Department, which helped form the agreement, said the funds would go to Alabama, Florida, Louisiana, Mississippi and Texas.
It will be used to clean up affected areas, including beaches.
Other recipients of the $1bn include the Department of the Interior and the National Oceanic and Atmosphere Administration.
Hundreds of miles of coastal wetlands and beaches were contaminated, a third of the Gulf’s US waters were closed to fishing, and the economic costs have reached into the tens of billions.
The Justice Department said the release of the money was the largest restoration agreement of its kind ever reached and was “a first step towards fulfilling BP’s obligations to fund the complete restoration of injured public resources”.
The department said the agreement does not affect the ultimate liability of BP or any other company for environmental damages or other liabilities, but lets restoration projects get started sooner.
The Secretary of the Interior, Ken Salazar, said in a statement: “This milestone agreement will allow us to jump-start restoration projects that will bring Gulf Coast marshes, wetlands and wildlife habitat back to health after the damage they suffered as a result of the Deepwater Horizon spill.”
Damaged seabirds and other wildlife including dolphins continue to wash up on beaches in the affected region. The agreement was announced the day after the first anniversary of the worst offshore oil spill in US history.
BP said on Wednesday it was suing Transocean, the owner of the oil rig that exploded in the Gulf of Mexico last year, for $40bn (£24.37bn) in damages.