The grounds, once home to George Canning, who died in 1827 after serving just 119 days as prime minister, will focus on a renewed terrace garden, a desilted lake with new islands and new paths.
Work to the landscape in Bracknell, Berkshire, will involve creating a more welcoming entrance, restoring an amphitheatre, improving landforms and planting trees, bushes and hedges.
South Hill Park is a 24ha grade II listed site. Contractors will lay hard and soft landscape and restore ornamental metalwork around the mansion, built in 1760. Other work will cover historic gateways and lake balustrades at the property.
"The open space in Birch Hill will be more welcoming and the landscape improved," said a representative for Gavin Jones. "This is a prestigious local project and we will conserve the park's key landscape features."
Heritage Lottery and the Big Lottery Fund awarded the £4.4m project a grant of £2.3m to help pay for the works as well as 10 years of ongoing upkeep.
The council's executive member for culture Iain McCracken said: "The park has long been seen as one of the jewels in Bracknell Forest's cultural crown."