More than $8bn (£6.5bn) has been pledged to help develop a coronavirus vaccine and fund research into the diagnosis and treatment of the disease.
Some 40 countries and donors took part in an online summit hosted by the EU.
EU Commission President Ursula von der Leyen said the money would help kickstart unprecedented global co-operation.
She said it showed the true value of unity and humanity, but warned much more would be needed in the days ahead.
In total, more than 30 countries, along with UN and philanthropic bodies and research institutes, made donations.
Donors also included pop singer Madonna, who pledged €1m ($1.1m), said Ms von der Leyen, who set out the Brussels-led initiative on Friday.
The European Commission pledged $1bn to fund research on a vaccine. Norway matched the European Commission's contribution, and France has pledged €500m, as have Saudi Arabia and Germany. Japan pledged more than $800m.
The US and Russia did not take part. China, where the virus originated in December, was represented by its ambassador to the European Union.
Of the money raised, $4.4bn will go on vaccine development, some $2bn on the search for a treatment and $1.6bn for producing tests, the EU said.
In her opening remarks at the summit, Ms von der Leyen said everyone must chip in to finance "a truly global endeavor".
"I believe 4 May will mark a turning point in our fight against coronavirus because today the world is coming together," she said.
"The partners are many, the goal is one: to defeat this virus."
UK Prime Minister Boris Johnson, another co-host of the conference, said the "more we pull together" in sharing expertise, "the faster our scientists will succeed" in developing a vaccine.
Johnson, who spent three nights in intensive care with Covid-19, was to confirm the UK's pledge of £388m for vaccine research, testing and treatment during the conference.
Along with the European Commission, the conference is being co-hosted by the UK, Canada, France, Germany, Italy, Japan, Norway and Saudi Arabia.
Emmanuel Macron and Angela Merkel, pictured last year, are among the world leaders who signed the letter
Italian Prime Minister Giuseppe Conte, French President Emmanuel Macron and German Chancellor Angela Merkel are also among those who have signed up to the initiative.
In the open letter published in weekend newspapers, the leaders said the funds raised would "kickstart an unprecedented global co-operation between scientists and regulators, industry and governments, international organizations, foundations and healthcare professionals".
"If we can develop a vaccine that is produced by the world, for the whole world, this will be a unique global public good of the 21st Century," they added.
At the same time, the signatories gave their backing to the World Health Organization in the face of US criticism of its handling of the outbreak.
Dozens of research projects trying to find a vaccine are currently underway across the world.
Even with more financial commitment, it will take time to know which ones might work and how well.
Most experts think it could take until mid-2021, about 12-18 months after the new virus first emerged, for a vaccine to become available.
A total of about $8 billion was promised by more than 30 countries and territories, including Japan, Canada and Saudi Arabia, on the first day of the pledging event.
European Commission President Ursula von der Leyen thanked donors for their support. She warned that this is only the beginning of the global fight against coronavirus, which requires a sustained effort.
Japan has pledged about $234 million dollars towards the development of a coronavirus vaccine.
The funds are set to be channeled through the Coalition for Epidemic Preparedness, or CEPI, and other groups.
Prime Minister Abe Shinzo made the pledge during a video message on Monday to a fundraising event led by the European Union.
Otherworld leaders pledged billions of dollars. The EU reports there are more than 70 vaccines in development around the world, but only a few have advanced to clinical trials.