A 2019 report by the International Union for Conservation of Nature's Cat Specialist Group found there is no longer a viable wildcat population living wild in Scotland.
Saving Wildcats, a six-year project supported by £3.2 million of EU funding, hopes to reintroduce the animals into the wild around the Cairngorms in 2023.
The project aims to prevent the extinction of the critically endangered species by breeding and releasing them into the wild.
Funding for the project has been hit by the covid pandemic, which forced the closures of Highland Wildlife Park and Edinburgh Zoo, costing RZSS over £1.5 million.
In addition to the £400,000 sum, RZSS has also received £278,000 from the Scottish Government's zoo and aquarium conservation fund.
Bosses said it will help ensure efforts can continue to protect other threatened native species, including the pine hoverfly, pond mud snail and flapper skate.
Dr Helen Senn, head of conservation and science programmes at RZSS said:"The past year has been an incredibly difficult time for our charity, with the closure of our parks for a total of five months cutting off our main source of income.
"While we still face significant financial pressures, this £678,000 Scottish Government funding to help protect native species and support our work with partners is very welcome."
"On top of the funding concerns, the project team have had to meet a series of practical challenges.
"These included delays to the construction of the breeding for release centre at Highland Wildlife Park, caused by the pandemic and severe winter weather.
"The breeding facility is now up and running in a secluded, off-show area at Highland Wildlife Park.
"Releasing carnivores to the wild is incredibly complex but we are planning to release the first wildcats in 2023, which will be very exciting."
Dr Jo Judge, CEO of the British and Irish Association of Zoos and Aquariums (BIAZA) said: "The iconic Scottish wildcat is on the very brink of extinction, but with support we can avoid a future without wildcats."