Background Childhood diarrhoea mortality has declined substantially in Peru in recent decades. We documented trends in childhood diarrhoea mortality from 1980 to 2015, along with trends in coverage of diarrhoea-related interventions and risk factors, to identify the main drivers of mortality reduction. Methods We conducted desk reviews on social determinants, policies and programmes, and diarrhoea-related interventions implemented during the study period. We reviewed different datasets on child mortality, and on coverage of diarrhoea-related interventions. We received input from individuals familiar with implementation of diarrhoea-related policies and programmes. We used the Lives Saved Tool (LiST) to help explain the reasons for the decline in diarrhoea mortality from 1980 to 2015 and to predict additional reduction with further scale up of diarrhoea-related interventions by 2030. Results. In Peru under-five diarrhoea mortality declined from 23.3 in 1980 to 0.8 per 1000 livebirths in 2015. The percentage of under-five diarrhea deaths as related to total under-five deaths was reduced from 17.8% in 1980 to 4.9% in 2015. Gross domestic product increased and poverty declined from 1990 to 2015. Access to improved water increased from 56% in 1986 to 79.3% in 2015. Oral rehydrating salts (ORS) use during an episode of diarrhea increased from 3.6% in 1986 to 32% in 2015. Vertical programmes focused on diarrhoea management with ORS were implemented successfully in the 1980s and 1990s, and were replaced by integrated crosscutting interventions since the early 2000s. LiST analyses showed that about half (53.9%) of the reduction in diarrhoea mortality could be attributed to improved water, sanitation and hygiene, 25.0% to direct diarrhoea interventions and 21.1% to nutrition. The remaining mortality could be reduced by three-quarters by 2030 with improved diarrhoea treatment and further with enhanced breastfeeding practices and reduction in stunting. LiST does not take into account the role of social determinants. Conclusions The reduction of diarrhoeal under-five mortality in Peru can be explained by a combination of factors, including improvement of social determinants, child nutrition, diarrhoea treatment with ORS and prevention with rotavirus vaccine and increased access to water and sanitation. The already low rate of diarrhoea mortality could be further reduced by a number of interventions, especially additional use of ORS and zinc for diarrhea treatment. Peru is a remarkable example of a country that was able to reduce childhood diarrhoea mortality by implementing interventions through vertical programmes initially, and afterwards through implementation of integrated multisectoral packages targeting prevalent illnesses and multi-causal problems like stunting.