Grosvenor Square will reopen to the public on Monday after undergoing a £25 million makeover.
One of central London's oldest and most famous public spaces, the square has been closed for a year while development work took place.
More than 150,000 new plants and 44 new trees now fill the park, along with winding paths, an education centre run by London Wildlife and a new cafe kiosk.
There are also two new wetland areas as well as 300 extra seats.
Wildlife is already returning, with ducks, butterflies and dragonflies all spotted in recent weeks.
It comes after decades of planning, with the traditional manicured grass and intersecting tarmac paths replaced with a “biodiverse haven”, according to those behind the project.
Elements of the landscaping have drawn inspiration from the square's original design.
Owned by the Grosvenor Group, the Duke of Westminster's private property company, Grosvenor Square closed last June to undergo its fourth major redesign since its construction in the first half of the 18th century.
Chief executive of Grosvenor Property UK Jamie Whitty-Lewis said: "We've truly revitalised it into a really special garden now."
"We are feeling the summers getting warmer and the winters getting wetter. The planting here has a cooling effect, so you'll feel right now it's actually quite cool here under the shade of the trees."
The Square can now absorb up to 1.4 million litres of stormwater at a time, doing its bit against urban flooding.
Chris Stanton, the lead landscape architect on the project, called it an "extraordinary transformation".
He said: "What we've managed to do is introduce a bit of the countryside back into the West End."
During a welcome address at the opening ceremony, the Duke of Westminster said: "We wanted a place that basically people came and stopped and were able to relax and sit, find their own space, be curious throughout the square, and enjoy it."
"I hope the way we've designed Grosvenor Square presents an opportunity for people just to relax a bit and find their own little area to sit away and have a moment to themselves."
First set out in the 1720s, Grosvenor Square was reserved for the use of the Square's residents, until it opened to the public after the Second World War.
The US Embassy overlooked the Square between 1938 and 2018, and it hosted a number of protests as a result, including against the Vietnam War.
