Population of the bird that has been an "inspiration for generations of poets and romantics", has drastically gone down by more than 90 percent in the last 40 years, says the study by the British Trust for Ornithology (BTO).
The bird would be upgraded to "red status" - signifying the highest degree of conservation concern, the Telegraph newspaper reported.
The nightingale's decline has been blamed on the population explosion of the muntjac deer, which has reduced the availability of the bird's habitat in the woods.
The muntjac is a small deer native to Asia, including Sri Lanka, India, China and Japan and was introduced to Britain by accident when some escaped in 1925 from the Duke of Bedfordshire's estate, which is now the Woburn Safari Park.
Pressures on its habitat in sub-Saharan African, where the bird goes during winters, as well as along its migration route to Britain have also contributed to the threat.
The bird is famous for its singing in the dark, and has been celebrated by poets since time immemorial.
The song - heard from mid-April to June, as male birds attract mates - was once familiar across southern England but is now no longer heard even in previous strongholds.
John Keats wrote "Ode to a Nightingale", inspired by a bird he heard in Hampstead, north London, in 1817.
Paul Stancliffe, from the trust, said: "We've looked at the rate of decline and continued it to make a prediction. In 10 years, the population is at a really, really low level. And then somewhere between 20 and 30 years it just drops off the bottom of the graph."
The trust is searching for solutions to halt the bird's extinction. It has launched the Nightingale Appeal and a CD of the bird singing, profits from which will go to research.
The CD features archive recordings of nightingales singing to the backdrop of World War II bombers over Britain.
