The memorial garden in Stratford will feature a ring of 33 blossom trees as its centrepiece, representing the impact of Covid-19 across the capital's 32 boroughs and the City of London.
Garden will be a "permanent reminder"
Revealing the plans, Khan said the memorial will invite Londoners to reflect on the pandemic, which has seen thousands of people lose their lives and "changed our capital forever".
He also hopes it will memorialise the positive ways in which the capital's citizens have come together in support of each other and key workers during the crisis.
"Covid-19 has had a devastating impact on our city and our country, and while we continue to battle the virus we are creating a lasting, living memorial to commemorate those who have lost their lives, pay tribute to the amazing work of our key workers and create a space for all Londoners to reflect on the experience of the pandemic," said Khan.
"This public garden of blossom trees will be a permanent reminder of the lives that have been lost, a tribute to every single key worker, and a symbol of how Londoners have stood together to help one another."
Project to be realised in one of London's worst-hit boroughs
Blossoming trees are to be used for the garden's centrepiece because this year's blossom season coincided with the start of the UK's first national lockdown.
Eight different species of trees will be used, planted together in three rings. The largest circle will have 17 trees, while the others will have nine and seven.
Local artist Junior Phipps is currently also developing a path and public benches to surround the site. Funding for the project will be provided by Bloomberg.
The London memorial garden is set to be planted in Queen Elizabeth Olympic Park in early 2021.
The site, which was originally built for the 2012 Summer Olympics, was chosen as it is in Newham – one of the capital's boroughs that was worst-hit by the pandemic.
Newham is also home to the BDP-designed NHS Nightingale Hospital, which was built in April within the ExCeL exhibition centre. The hospital is among several temporary healthcare facilities around the world that were built to help increase intensive-care capacity during the pandemic.
Memorial garden is part of scheme to bring nature to cities
The memorial garden forms the first part of a wider campaign being carried out by the National Trust over the next few years to give more people in the UK access to nature.
This follows a sharp rise in awareness of the need for nature in our lives, prompted by the pandemic and people having to quarantine without access to the outside.
"This space will thrive and become more beautiful as the trees grow and become part of their surroundings," said Nicola Briggs, a director at the National Trust.
"We want to work hard to ensure that together we design something that is appropriate for the neighbouring communities; somewhere that becomes a space for reflection as well as bringing nature and beauty to more people."
Ukranian architect Sergey Makhno has commented on this experience, saying that the pandemic will encourage a rise in urban farming. Architect Cristina Monteiro said it should "inspire us to rewild cities to better support our children".
Garden latest in string of memorial proposals
Khan's announcement for the memorial garden is the latest in a string of proposals being developed to honour those that have lost their lives during the coronavirus pandemic.
These include the nature-focused proposal by Italian architect Angelo Renna, which imagines 35,000 cypress trees being planted in Milan's San Siro stadium.
Latin American architecture firm Gómez Platero recently unveiled a design for a circular monument named the World Memorial to the Pandemic, which would take the form of a large sculpture installed on water off the coast of Uruguay.
Main photo of the Olympic Park is by Tom Wheatley via Unsplash.