Throughout East Africa, cattle play important roles in livelihoods of the rural poor and in supporting urban food security. As a result of low productivity, the dairy sector emits as much as 20 times more greenhouse gas (GHG) emissions per unit product than high income countries, while also acting as a leading driver of emissions from land use change. Productivity improvements may contribute to domestic food security and poverty alleviation jointly with GHG reductions for national climate targets. Yet the multi-functional roles cattle play within livelihoods imply mitigation strategies must be designed with care. Using household survey data from Kenya and Tanzania and a system modelling framework, this thesis evaluates options to better align country dairy policy initiatives with GHG targets under nationally determined contributions (NDCs). The thesis includes an empirical chapter (3) informing of variability in GHG emissions and dairy production practices across Kenya and Tanzania to inform mitigation interventions. Two model chapters then assess respectively the potential of feeding efficiency gains (chapter 4) and genetic gains combined with improved feeding (chapter 5) to contribute to GHG reductions consistent with development targets envisaged by the ‘dairy roadmap’ (part of the 2016 ‘Livestock Master Plan’). Feeding efficiency gains alone have negligible potential to meet climate targets consistent with growth in milk production (chapter 3). Instead, realising milk production targets with absolute reductions in GHG emissions will depend on reaching ambitious breed adoption targets (chapter 4). Realising such targets could increase milk production to 70% and 100% of the national target with respectively 29.6 ± 13.4% (95% CI) and 13.8 ± 17.1% GHG reductions relative to the baseline. Cost-benefit accounting indicates improved breeds would have net positive welfare impacts, increasing income on average by 195 to 261 USD capita-1 year-1 for producers. Since genetic gains are a central feature of Tanzania’s dairy roadmap, the findings demonstrate the likely congruence between climate mitigation and national dairy development initiatives in East Africa, suggesting that improved breeds can deliver both climate and livelihood benefits within high agro-ecologic potential systems of East Africa.