International trade poses a serious and growing threat to biosecurity through the introduction of invasive pests and disease: these have adverse impacts on plant and animal health and public goods such as biodiversity, as well as food production capacity. While international governmental bodies such as the World Trade Organization (WTO) recognise such threats, and permit governments to protect human, animal, and plant life or health, such measures must not be applied in a way that is restrictive to trade. This raises a fundamental (but little-examined) tension between effective biosecurity governance and the neoliberal priorities of international trade. In this paper we examine how such tensions play out in the different political and geographical contexts of Australia and the United Kingdom. A comparative approach enables close scrutiny of how trade liberalisation and biosecurity are coconstituted as compatible objectives as well as the tensions and contradictions involved in making these domains a single governable problem. The comparative analysis draws attention to the policy challenges facing Australia and the UK in governing national biosecurity in a neoliberal world.These challenges reveal a complex geopolitics in the ways in which biosecurity is practised, institutionalised, and debated in each country, with implications for which pests and diseases are defined as threats and, therefore, which commodities are permitted to move across national borders. Despite efforts by the WTO to govern biosecurity as a technical matter of risk assessment and management, and to harmonise national practices, we contend that actual biosecurity practices continue to diverge between states depending on perceptions of risk and hazard, both to agricultural production and to rural environments as a whole, as well as unresolved tensions between internationalised neoliberalism and domestic concerns.