The three Western allies said they would develop the cable to provide faster internet to Nauru, Kiribati and the Federated States of Micronesia.
"This will support increased economic growth, drive development opportunities, and help to improve living standards as the region recovers from the severe impacts of Covid-19," a joint statement from the United States, Japan and Australia said.
The three allies did not specify how much the project will cost.
The development of the undersea cable is the latest funding commitment from the Western allies in the telecommunications sector of the Pacific.
The United States and its Indo-Pacific allies are concerned that cables laid by the People's Republic of China could compromise regional security. Beijing has denied any intent to use commercial fiber-optic cables, which have far greater data capacity than satellites, for spying.
Australia in 2017 spent about AUD, U137 million ($98.2 million) to develop better internet access for the Solomon Islands and Papua New Guinea.