Australians have long enlisted in overseas armed forces, and Australia does not criminalise foreign military service as such. However, recent cases highlight the complex legal and diplomatic consequences that can arise when Australian nationals fight in foreign conflicts.
One such case is that of Oscar Jenkins, a former Melbourne schoolteacher who enlisted in Ukraine’s International Legion and was captured by Russian forces in December 2024. He was charged as a mercenary and sentenced to 13 years’ imprisonment in a Russian maximum-security prison. Australia has called on Russia to respect Jenkin’s lawful prisoner-of-war status and continues to pursue diplomatic avenues for his release.
The case underscores a central legal reality: Australia’s international obligations and its own domestic criminal laws do not stop at the border when its nationals enlist in foreign armed forces.
Combatants or mercenaries: why legal status matters
When a foreigner actively participates in an armed conflict, their legal status under international humanitarian law determines whether they may lawfully fight, what protections they receive if captured, and whether they are immune from prosecution for lawful acts of war.
International humanitarian law defines combatants as members of the armed forces of a party to the conflict. Combatants may participate directly in hostilities and, if captured, are entitled to prisoner-of-war status. That status carries strict protections, including humane treatment, access to food and medical care, and protection from torture.
Combatants are immune from prosecution for lawful participation in the hostilities, provided they comply with the laws of war. Where combatants are accused of war crimes, international humanitarian law requires fundamental fair-trial guarantees, including the right to understand the charges, access legal representation and consular assistance, challenge evidence, and be tried before a lawfully constituted and impartial court.
Mercenaries are defined more narrowly. To be classified as a mercenary, an individual must meet all the elements of the definition, including being recruited to fight, not being a national or resident of a party to the conflict, not being a part of the official armed forces, and being motivated by private gain. Mercenaries, do not enjoy lawful combatant status, are not permitted to participate directly in hostilities, and are not entitled to prisoner-of-war protections if captured.
Australian foreign volunteers such as Oscar Jenkins and Kallen Benjamin Lewis, who responded to Ukraine’s call for international volunteers, were officially sworn into Ukraine’s armed forces and paid on the same basis as Ukrainian nationals of equivalent rank. That fact alone means they do not meet the international humanitarian definition of a mercenary.
Russia’s rejection of POW status
Despite this, Russia has maintained that it will treat foreign fighters in Ukraine as mercenaries. On that basis, Russia has denied them prisoner-of-war status and immunity from prosecution for what would otherwise be lawful participation in hostilities.
Before courts operating in the self-proclaimed Luhansk People’s Republic in Russian-occupied eastern Ukraine, foreign fighters have been subjected to proceedings conducted behind closed doors, sometimes in absentia, with limited access to legal advice and allegations of torture, threats and forced confessions. These proceedings have been widely criticised as lacking basic due process guarantees.
Several foreign fighters captured in 2022 were branded as mercenaries and sentenced to death. The European Court of Human Rights ordered interim measures against Russia to protect their lives, and only an eleventh-hour prisoner exchange, reportedly mediated by Saudi Crown Prince Mohammed bin Salman, secured their return home.
Oscar Jenkins has not been so fortunate. Kallen Lewis, sentenced in absentia to 14 years’ imprisonment, has reportedly been placed on an international wanted list. These cases demonstrate that the legal classification of foreign fighters is not an abstract question. It has a direct impact on what Australia can do to protect its nationals and the diplomatic costs of those efforts.
What Australia can do when an Australian is captured
Australia’s options when an Australian foreign fighter is detained abroad are limited, but they are not non-existent. Through its embassies, Australia may seek consular and welfare access and engage with the International Committee for the Red Cross to request access where prisoner-of-war status or humane treatment is being denied.
Australia may also raise cases through parliamentary statements and international forums, including the United Nations General Assembly, while pursuing quiet diplomatic engagement aimed at improving conditions or securing release. Collaboration with the United Nations Working Group on Arbitrary Detention and organisations like Amnesty International can increase international scrutiny and pressure.
Taken together, these measures reflect a difficult reality: Australia cannot compel a detaining power to comply with international humanitarian law. It can, however, insist publicly and persistently that the international humanitarian law framework applies and keep cases diplomatically active to increase the prospects of humane treatment and eventual release.
A difficult but unavoidable balance
To protect Australians detained unlawfully abroad, Australia must insist on the rule of law in armed conflict, including prisoner-of-war protections and fair trial guarantees.
At the same time, consistent adherence to international humanitarian law requires that Australia does not shield its own nationals from accountability for international crimes committed during foreign service. The Brereton report exposed Australia’s slow response to alleged war crimes committed by Australian Defence Force personnel in Afghanistan between 2005 and 2012. It took more than a decade for the first Australian soldier to be charged.
Conclusion
Foreign military service by Australians is unlikely to diminish and is becoming increasingly legally complex. Australia’s obligations in this area are therefore twofold.
First, Australia must protect its foreign fighters from unlawful treatment by insisting clearly, consistently and publicly on the application of international humanitarian law, including prisoner-of-war protections where they apply and minimum fair-trial guarantees where they do not. That includes challenging sham proceedings and unlawful classifications.
Second, Australia must demonstrate genuine adherence to international humanitarian law by ensuring that its own nationals are not shielded from accountability where credible allegations arise, domestic investigative and prosecutorial pathways must be capable of responding effectively. A coherent framework for foreign military service should therefore include clear upfront warnings to Australians about the legal risks of enlistment, the consequences of capture, and the reality that foreign armed service does not confer immunity from international criminal responsibility. Australia’s legal obligations follow its nationals into battle, into captivity, and, where necessary, back into Australian courts.
