Fundamental economic and societal transformations are necessary to avoid dangerous climate change. One broad policy approach that addresses the close relationship between conservation and climate change mitigation is based on correcting a market failure, that is, to establish a price signal for carbon, or more generally, greenhouse gas emissions. While many synergies between climate policy instruments and biodiversity conservation do exist, current policies often fall short of harvesting this potential. Here, we present six key challenges: (1) establishing a strong price signal for greenhouse gas emissions from all emission sources (including land-use and the terrestrial biosphere) that takes into account long-term societal and ecological costs; (2) expand carbon market instruments to cover the full range of greenhouse gases; (3) develop an ambitious, yet accountable architecture for rising emission prices; (4) develop guidelines and ensure enforcement to avoid greenhouse gas leakage; (5) improve greenhouse gas emission measurements from land-use and the biosphere; and (6) integrate emission reduction as a priority into relevant policies. Substantial synergies, but also trade-offs between climate policy and conservation exist, and we identify key risks and challenges. We call for (1) evidence-based evaluations of policy options; (2) avoiding too narrow framings of contested issues such as forest plantations, biofuels, or land-use decisions that exclude (or downplay) indirect effects (e.g., indirect land-use changes or creating carbon debts); and (3) strengthening integrated analyzes beyond sector policy goals. We conclude that avoiding bio-perverse impacts of climate policies on biodiversity will be crucial for the success of global climate change mitigation.