‘Mainstreaming’ climate change by embedding climate change considerations in government policies, processes, and operations can bolster the realization of climate mitigation and adaptation goals and reduce risks of counter-productive actions. Some climate laws around the world now contain explicit mainstreaming duties, in parallel with emissions reduction targets and adaptation planning requirements. This article proposes a conceptual model for climate change mainstreaming in government, with two pillars. Firstly, it defines objectives of climate mainstreaming, emphasizing that mainstreaming activities occur along a spectrum of ambition towards a goal of ‘mature mainstreaming’. Secondly, it proposes three complementary pathways to mature mainstreaming – regulatory, institutional, and capacity and capability-building pathways – to classify mainstreaming activities, and barriers to and enablers of mainstreaming. Grounded in empirical insights from a leading jurisdiction (Victoria, Australia), the model can assist governments to clearly articulate mainstreaming objectives and to identify, prioritize, and monitor mainstreaming initiatives to help in achieving their climate policy goals.