The Department of Health announced today that adults and teenagers with severe COVID-19 will be allowed to be treated with remdesivir if they fit specific criteria.
This makes the drug, which destroys a part of the virus in order to stop it reproducing, the closest thing doctors have to a cure or treatment for the disease.
The criteria for who will get it have not been laid out by the Government but doctors will be expected to decide on a case-by-case basis who is most likely to benefit.
Early trials of remdesivir have suggested that it can speed up people's time to recovery by four days, British officials said.
Doctors in the US and Japan are already using the medication to treat COVID-19 patients under emergency access schemes, and the UK is now following suit in the face of incontrovertible scientific evidence.
It is expected to be available immediately to patients across England, Wales, Scotland and Northern Ireland.
Lord James Bethell, Government minister for innovation, said: 'This shows fantastic progress.
'As we navigate this unprecedented period, we must be on the front foot of the latest medical advancements, while always ensuring patient safety remains a top priority.
'The latest, expert scientific advice is at the heart of every decision we make, and we will continue to monitor remdesivir’s success in clinical trials across the country to ensure the best results for UK patients.'
Remdesivir, which is produced by the California-based company Gilead Sciences, has been approved under the Early Access to Medicines Scheme (EAMS).
Britain's Medicines and Healthcare products Regulatory Agency (MHRA) gave the go-ahead for NHS doctors to use it on people who are seriously ill with COVID-19.
Officials said: 'Allocation of the drug will be based on expert clinical advice and will take into consideration the situation where it is most likely to provide the greatest benefit.'
The MHRA's green light means the drug can be used before it has been officially licensed for a prescription.
Usually, drugs have to go through lengthy testing and approval processes which take into account large amounts of scientific evidence and cost-effectiveness.
MHRA chief executive, Dr. June Raine, said: 'We are committed to ensuring that patients can have fast access to promising new treatments for COVID-19.
'We will continue to work closely with the Department of Health and Social Care and other healthcare partners on protecting public health in the UK by prioritizing our essential work on clinical trials, access to medicines, and the development of vaccines.'
Remdesivir is the first medication to get approval for use outside of a clinical trial in the UK.
It is an antiviral drug that works by crippling an enzyme called RNA polymerase, which is vital for the virus to reproduce and spread. By damaging this, the drug may be able to stop the coronavirus in its tracks.
Other drugs that work in different ways are being used on NHS patients are part of clinical trials, but these are much less available.
Only limited numbers of people can be enrolled in trials and only certain people - usually otherwise healthy patients - are eligible for them.
For those who do make it onto trials there is often still a 50/50 chance that they get a placebo - a fake drug - anyway.
The two major clinical trials underway in Britain are named Recovery and REMAP-CAP.
On Recovery, which is being led by the University of Oxford but taking place across the country, patients may be given one of the following drugs:
Doctors are also testing whether people benefit from a treatment called convalescent plasma, in which patients are given part of the blood of someone who has already recovered from the virus.
This, it is hoped, could introduce the antibodies - disease-fighting substances - needed to fend off the disease and bypass the body's own process of developing them, which takes weeks after infection.
It is less clear which medicines are being used in the REMAP-CAP trial.