ABSTRACT To reduce the energy sector’s CO2 emissions, sustainability transitions are essential but may have unexpected national security consequences. We investigate policymaking around energy transitions and national security, combining sociology with sustainability transitions thinking to analyse 73 policy documents issued between 2006 and 2023 in Estonia, Finland, and Norway and investigate how zero-carbon energy and security issues have co-evolved with, strengthened, or undermined one another by analysing the rhetoric in official national strategy documents. With an epistemic governance framework, we identify the discourses that contextualise, justify, and explain policymaking in the energy–security nexus. We find that sustainable energy transitions are strengthened by connections to national security when alternative energy niches have matured but undermined for the same reason when fossil fuels are viewed as more robust sources of security. We detect policy intervention points aiming to indicate how transitions are enabled. Estonia and Finland evince strategic directions to destabilise the regime while supporting niches, whereas Norway focuses on continued oil and gas production. Whereas all are in principle in favour of sustainability transitions, they define transitions differently: Estonia values national sovereignty, Finland preparedness and the economy, and Norway sustainable development and economic security tied to hydrocarbons.