Dili and Canberra have been at loggerheads for a decade over the Certain Maritime Arrangements in the Timor Sea (CMATS) agreement, which carved up future revenue from oil and gas reserves in the area.
The matter was before the Permanent Court of Arbitration and in a statement the Hague-based body said agreement had been reached "on the central elements of a maritime boundary delimitation between them in the Timor Sea".
Several matters still need to be thrashed out and "until all issues are resolved, the details of the parties' agreement will remain confidential", it added.
Impoverished East Timor, also known as Timor-Leste and which gained independence from Indonesian occupation in 2002, relies heavily on oil and gas exports.
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In 2006 it signed the CMATS treaty with Australia, which covers the vast Greater Sunrise gas field between the two nations that is worth billions of dollars.
But Dili later accused Canberra of spying to gain commercial advantage during the 2004 negotiations and demanded the treaty be ripped up.
Australia had argued the treaty was legal, binding and valid, but agreed to end it in line with Dili's wishes on January 9.
"This agreement, which supports the national interest of both our nations, further strengthens the long-standing and deep ties between our governments and our people," she said.
East Timor delegation head Xanana Gusmao, the country's former president, echoed those sentiments, hailing the pact after "a long and at times difficult process".
"This is an historic agreement and marks the beginning of a new era in Timor-Leste's friendship with Australia," he said.