Gillard said she had "very constructive" discussions with US President Barack Obama about the Trans-Pacific Strategic Economic Partnership (TPP), on the sidelines of the East Asia Summit in the Cambodian capital.
"The ambition here is for the agreement to be reached by October,"she said.
The partnership currently counts Brunei, Singapore, New Zealandand Chile as full members, with countries in formal negotiations to join including the United States, Canada, Australia, Vietnam and Malaysia.
Its rules require members to eliminate tariffs, end subsidies to domestic firms and allow foreign exporters and investors free market access.
"President Obama was very clear about the high level of ambition that is being sought in this agreement," she said.
Negotiations on another deal, the Regional Comprehensive Economic Partnership, were also to be launched Tuesday, according to an official schedule.
"From our perspective it makes sense to be involved in both and to be maximizing our efforts in both," Gillard said.//DPA