Policy decision making for agricultural greenhouse gas mitigation is hindered by scientific uncertainty regarding the effectiveness of mitigation measures. Successful on-farm adoption of measures is contingent upon farmer perception of the relative practicality of implementing the measure and associated incentives and advice. In the absence of a comprehensive evidence base we utilised Best–Worst Scaling, a discrete choice survey method, to elicit expert and farmer opinion on the relative effectiveness and practicality of mitigation measures to reduce greenhouse gas emissions from sheep production systems. The method enabled individual mitigation measures to be ranked on a ratio scale of effectiveness (expert opinion) and practicality (farmer opinion). Six measures were identified as possessing the combined qualities of effectiveness and practicality and are considered priority candidates for policy promotion. The overall preferred measure was the use of legumes in pasture reseed mixes. Estimation and analysis of the distribution of individual respondent scores revealed heterogeneity in farmers’ perceptions of practicality, suggesting that flexible policies are required to enable farmers to select mitigation measures most suited to their farm type and locality. Practical measures with below average effectiveness may be widely adopted with limited regulation, incentivisation or advice, whilst some highly effective measures with lower practicality are likely to present greater obstacles to adoption.