At least 2,000 patients will receive the new treatment in a clinical trial.
The new treatment uses man-made antibodies, which act like human antibodies in the immune system, to try and lessen the impact of Covid-19.
The Recovery trial, co-ordinated by the University of Oxford, will assess the impact of giving patients REGN-COV2 alongside usual standard care to see if it lessens the severity of Covid-19 and can reduce deaths.
In June, the Recovery trial, which includes 176 UK hospital sites, found that a cheap steroid called dexamethasone could save the lives of people with severe Covid infection.
In the new phase 3 study, at least 2,000 patients will be randomly allocated to receive REGN-COV2 plus usual care, and the results will be compared with at least 2,000 patients not on the therapy.
REGN-COV2, which was created by the US firm Regeneron, is made up of two monoclonal antibodies (REGN10933 and REGN10987).
The cocktail of drugs targets two components in the spike protein of the Covid-19 virus with the aim of interrupting its ability to infect.
Peter Horby, professor of emerging infectious diseases and global health at the University of Oxford and chief investigator of the trial, said: “We have already discovered that one treatment, dexamethasone, benefits Covid-19 patients, but the death rate remains too high so we must keep searching for others.
“The Recovery trial was specifically designed so that when promising investigational drugs such as REGN-COV2 became available they can be tested quickly.
“We are looking forward to seeing whether REGN-COV2 is safe and effective in the context of a large-scale randomised clinical trial.
“This is the only way to be certain about whether it works as a treatment for Covid-19.”
Nick Cammack, who is leading Covid-19 therapeutics work for Wellcome, said: “Novel antivirals and monoclonal antibodies are among the most exciting and promising treatments for Covid-19 because they are specific to the disease, but they are also traditionally the most expensive.
“Large-scale randomised controlled studies like Recovery give us the best understanding of whether drugs like REGN-COV2 are safe and effective against Covid-19, but we must ensure that any successful treatment is available to everyone who needs it globally.”
England’s deputy chief medical officer, Professor Jonathan Van-Tam, said: “Today’s news is another promising step in the search to find effective treatments, which will improve our ability to deal with this destructive virus, and a testament to the confidence that others around the world have in this brilliantly conceived and executed trial.
“I look forward to seeing how REGN-COV2 performs in clinical trials, and I urge people to volunteer in this research which could ultimately save many lives."