About 29 properties will start opening from June 3 for people who have booked tickets in advance to limit numbers and keep the public safe. More attractions will open over the summer at sites where social distancing can be observed, and with only a third of the normal number of visitors allowed. The reopening will be for sites in England and Northern Ireland.
The National Trust warned that all properties and car parks in Wales remain closed in line with Welsh government rules.
All Trust houses and shops remain closed, along with holiday cottages and campsites.
While coastal and countryside car parks are mostly open, some busier ones may need to be closed or pre-booked, the charity has said.
Booking for parks and gardens opens today via the National Trust website, and will be free for Trust charity members.
The charity, which said sites will display information on how to stay safe, is also urging people to limit how many visits they book for now and to avoid busy hotspots.
The Royal Horticultural Society is also reopening its gardens around England from June 1 with a pre-booked tickets system.
The moves come after the Government amended regulations to confirm that people in England can visit gardens and land maintained for public use.
In Northern Ireland, the Executive has permitted the reopening of outdoor spaces.
Attingham Park, Shropshire
Belton House, Lincolnshire
Clumber Park, Nottinghamshire
Calke Abbey, Derbyshire
London and the South East
Hinton Ampner, Hampshire
Polesden Lacey, Surrey
Scotney Castle, Kent
Sissinghurst Castle Garden, Kent
Standen House and Garden, West Sussex
Sheffield Park and Garden, East Sussex
The Vyne, Hampshire
Beningbrough Hall, North Yorkshire
Gibside, Tyne & Wear
Dunham Massey, Greater Manchester
Quarry Bank, Cheshire
East of England
Anglesey Abbey, Gardens and Lode Mill, Cambridgeshire
Sutton Hoo, Suffolk
Wimpole Estate, Cambridgeshire
Castle Coole, County Fermanagh
Castle Ward, County Down
Downhill Demesne and Hezlett House, County Londonderry
Florence Court, County Fermanagh
Mount Stewart, County Down
Portstewart Strand, County Londonderry
Rowallane Garden, County Down
The Argory, County Armagh