The Heritage Lottery Fund (HLF) is giving a £3.9 million grant towards the ambitious project.
The castle grounds in Stornoway are popular with walkers, joggers, families and as venues for outdoor summer events.
The total cost is nearly £5.5 million and will restore important historic features, including the formal gardens, improve access, enhance management and maintenance and provide new facilities to encourage more people to enjoy the outstanding public park.
Head of the Heritage Lottery Fund in Scotland, Colin McLean, said: “Our parks, and the historic features in them, are a wonderful legacy from our ancestors. They are enjoyed by all ages and are often a community’s only green space in which to relax away from the pressures of daily life.
"Using funds raised through the National Lottery, HLF is able to protect these precious places helping make a difference to the quality of life for millions of Scots.”
Lews Castle Grounds is the only historic park on the Western Isles and is ranked as ‘outstanding’ in the Inventory of Gardens and Designed Landscapes.
The park, which forms the iconic backdrop to Stornoway harbour, is owned by the Stornoway Trust for the community.
It includes formal gardens, ornamental planting, carriage drives and paths and extensive woodland making it dramatically different from the rest of the rugged island landscape.
The project aims to encourage more people to use the grounds with better access and restored historic features which are currently at risk of being lost.
It will also complement wider regeneration initiatives such as the redevelopment of Lews Castle.
It is anticipated the rest of the cash will come from contributions from the Stornoway Trust, the Comhairle, Historic Scotland and European funding.
£3.9 million grant to help improve Lews Castle grounds
2 July 2015
A major chunk of the cash needed to improve the Lews Castle Grounds has been awarded.