Background: Mimosa diplotricha is an emerging or established weed in many parts of the world, including many countries in Africa, where it is impacting on biodiversity, crop and pasture production, and driving socio-ecological change. Objectives: To establish the current distribution of M. diplotricha in eastern and southern Africa and its impacts on livelihoods in northern Malawi. Methods: Records on current distribution were collected from roadside surveys, literature reviews and herbarium data. Household surveys were conducted in the Karonga District, Malawi, to understand its impacts on local livelihoods. Results: Mimosa diplotricha is abundant in western Ethiopia, southern Tanzania, and northern and southeastern Malawi with isolated populations in western Rwanda, Burundi, Mozambique, and on the northern shores of Lake Victoria in Uganda. Most respondents said that M. diplotricha invasions were reducing the amount of grass and shrubs in rangelands, with over half saying it reduced crop yields. This invasive plant is also reducing the availability of medicinal plants and other natural resources. Conclusions: Mimosa diplotricha has the potential to significantly expand its range in eastern Africa, and parts of southern Africa, and as such there is an urgent need to develop and implement an integrated management strategy, including biological control, to reduce the negative effects of this invasive plant on local livelihoods.