Japanese Prime Minister Shinzo Abe met his Australian counterpart Malcolm Turnbull in Sydney on Saturday where the pair agreed to deepen defence ties and stressed the importance of the Trans-Pacific Partnership (TPP).
Abe's visit comes amid heightened regional tension in the South China Sea and fears US President-elect Donald Trump will push ahead with his pledge to kill the trade agreement once he takes office on January 20.
"We have confirmed our commitment to the rule of law, free trade and open markets in our region," Turnbull told reporters at a joint press conference.
Abe said the increasingly uncertain geopolitical landscape made the relationship between Japan and Australia more important than ever.
"It is important to guard and increase the robustness of the free, open and rules-based international order," Abe said.
Both leaders spoke of their desire to see the TPP ratified, despite opposition from Trump.
The 12-member pact aims to cut barriers in some of Asia's fastest-growing economies, but it does not include China.
Without US approval the agreement cannot come to fruition.
Following bilateral talks, the two leaders announced the signing of an Acquisition and Cross-Servicing Agreement (ACSA), which will increase cooperation in combined military exercises, training and peace-keeping operations. The agreement is expected to be finalised by the end of 2017.
The announcement comes nearly nine months after Australia chose a French bid over a Japanese design for a new fleet of submarines.
The loss of the $40 billion contract was a major blow for Abe's ambitions to develop Japan's defence export capabilities as part of a more muscular security agenda.
Japan, as well as Australia, is looking to protect its strategic and trade interests in the Asia-Pacific region, especially as China becomes increasingly assertive in the South and East China Seas.
Both leaders also reaffirmed the importance of their respective security alliances with the United States.
China's recent naval exercises in the South China Sea and the building of islands there, with military assets, have unnerved its neighbours and risk provoking a reaction from the United States.
Trump's nominee for secretary of state, Rex Tillerson, has said China should be denied access to islands it has built in the South China Sea.
China claims most of the resource-rich sea, through which about $5 trillion in ship-borne trade passes every year. Neighbours Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.
