England's ninth national park, stretching from Winchester to Beachy Head along the south coast, has been given the green light from Environment Secretary Hilary Benn following a lengthy inquiry.
South Downs National Park will cover 1,623 square kilometres and a government authority to run the park will be formed by April 2010 and become fully operational a year later.
The measure means the chalky hills of the southeast coast of England will receive government funds and be protected better from commercial development.
England's eight other national parks, which include the Lake District, the Peak District and Dartmoor, are due to receive about £47m of funding this year.
"National Park status can be a real boost for the local economy, attracting new visitors, businesses and investment," said Hilary Benn. "Above all, the South Downs' wonderful countryside will be protected forever for the enjoyment of everyone."