Suffolk Wildlife Trust has raised the £100,000 it needs to buy Knettishall Heath country park.
The money will be used alongside £720,000 from the Heritage Lottery Fund and a "generous" legacy donation.
The heath, which is leased and managed by Suffolk County Council, is being sold by its private owner.
Julian Roughton, the trust's chief executive, said the purchase would "secure the future of Knettishall Heath as a haven for wildlife and people".
The trust had said it needed to raise the money by the end of January but required just over a week to meet its target.
"Reaching £100,000 so quickly is a huge achievement and we want to thank everyone for their support," said Mr Roughton.
"Well over 1,000 people sent in donations and many included memories and stories about Knettishall Heath and its importance to their family."
The park, which is owned by the Riddlesworth Estate, is a mixture of heath, woods and meadow in The Brecks covering 388 acres (157 hectares).
The county council said it would give neighbouring meadowland it owns as a gift to the trust which would increase the size of the country park to 434 acres (176 hectares).
The Conservative-run council said it spent £350,000 a year on country parks and needed to save £50m over the next two years due to cuts in its funding from central government.
The trust said donations were still being accepted and would be used to buy ponies for the land and support the conservation work.