The joint commitment was made following the first leaders' meeting of the so-called Quad - a group formed in 2007.
The vaccines - expected to be the single-dose Johnson & Johnson product - are set to be manufactured in India.
The US said the "massive joint commitment" would initially focus on delivering doses to South East Asia.
"With Indian manufacturing, US technology, Japanese and American financing and Australian logistics... [we] committed to delivering up to one billion doses," US National Security Adviser Jake Sullivan said shortly after the virtual summit on Friday.
He said the vaccines would go to the Association of South East Asian Nations (Asean) as well as "the Pacific and beyond".
The Indian company Biological Ltd will manufacture the extra doses of the Johnson & Johnson jab, which received initial World Health Organization (WHO) approval on Friday.