The South Downs National Park Authority will have 27 members, including one from Brighton and Hove City Council.
The size – and the make up – of the authority has been set out in a ministerial statement by Hilary Benn, the Secretary of State for Environment, Food and Rural Affairs.
He said that the new authority would consist of 27 members.
Local authorities are to have a majority, with 14 members.
Six members will be nominated by parish councils while Mr Benn will appoint the remaining seven members to represent the national interest.
Mr Benn said: “To ensure that the national park authority keeps in close touch with communities and is able to respond to their concerns, I expect the authority to place a big emphasis on community and stakeholder engagement.
“I shall now include the 27-member authority in the statutory instrument which I shall lay before Parliament around the turn of the year.
“With Parliament’s consent, this will allow the national park authority to be established from 1 April 2010 and to become operational from 1 April 2011.”
Robin Crane, chairman of the South Downs Campaign, said: “This is another important step towards setting up a national park authority to look after the South Downs.
“While Hilary Benn confirmed the boundary of the national park last month, at that stage he did not say how it was going to be managed.
“Now he has made the decision on this, we can move forward.
“We very much welcome Hilary Benn’s statement that he expects the new authority to engage closely with local communities and stakeholders.
“This will be essential if the national park authority is going to be successful in protecting and enhancing the South Downs.”