Domestic counter-terrorism legislation can undermine States’ obligations in relation to both respecting and ensuring respect for the Geneva Conventions of August 1949 (GCs) and their Additional Protocols (APs). As a middle power with a dualist, common law legal tradition, the Australian experience is a useful case study. In its counter-terrorism regime, there is an absence of suitable exemptions for certain kinds of training, and an overly conservative approach to terrorism financing risk within the humanitarian sector. Problematic also is the legislation’s presumably inadvertent erosion of the principle of the equality of belligerents. Further, in recent citizenship changes relating to counter-terrorism, Australia could be relying on a third party to investigate and prosecute serious violations of the GC or APs. In doing so, Australia’s broader application of its Common Article 1 (CA1) obligations are undermined and by extension, so too is its moral authority to influence other States in efforts to ensure respect for these instruments. There are a number of practical measures that States – and their citizens – can take to avoid these problematic developments. Decision-makers, civil servants and the judiciary all have a role in developing, applying and interpreting domestic counter-terrorism laws and must be aware of how this framework interrelates with international humanitarian law (IHL) principles and CA1 obligations to ensure that an appropriate balance is found between legitimate security concerns and the protection of fundamental principles of IHL. Civil society, particularly the humanitarian sector and Red Cross and Red Crescent National Societies, has an important role to play in debates and development of domestic counter-terrorism measures, alongside other key influencers such as the legal and academic sectors.