Despite tremendous advances in the fight against infectious illnesses, the disease burden in under-five children remains significant, particularly in low- and middle-income countries (LMICs). Low-cost preventive measures like breastfeeding, water, sanitation, and hygiene (WASH), and immunization are important public health interventions for avoiding under-five deaths. The main objectives of this study are to identify the amenable under-five deaths, and the causes responsible for these amenable deaths, and prioritize the high-impact interventions using the Equitable Impact Sensitive Tool (EQUIST) in Bangladesh. Data were collected and validated for more than 300 variables and nearly 300 intervention and coverage indicators for bottleneck analysis. One five-day long workshop, one two-day long and one three-day long workshop were held to collect and validate the data and to conduct the bottleneck analysis using the Tanahashi model. The results of the frontier analysis show that the key epidemiological causes that are responsible for inequity in the under-five mortality rate are diarrhoea, asphyxia, pneumonia, sepsis and prematurity in Bangladesh in 2020. The high-impact intervention packages which could contribute to reducing the existing disparities in the under-five mortality rate are WASH, delivery by skilled professionals, antenatal care, integrated management of neonatal and child illnesses (IMNCI) and immunization plus. The high-impact interventions that are expected to contribute to reducing the existing disparities in cases of stunting are improved sanitation, hand washing with soap, improved water sources and balanced energy supplementation. WASH and delivery by skilled professionals are major interventions capable of averting the highest number of under-five deaths in Bangladesh.