Background: Globally, child mortality estimates are more clustered among the developing countries where quality data on estimates and determinants of child mortality are compromised. To achieve sustainability in reducing child mortality estimates, the integrated Verbal Autopsy and Social Autopsy (VASA) tool help in estimating prevalence and assigning medical and social causes and determinants of child survival, especially in the developing countries. A validation study of the Child Health Epidemiology Reference Group’s (CHERG) Verbal autopsy/Social Autopsy (VASA) tool has been undertaken for employing in a Karachi VASA Integrated Child Mortality Investigation-ICMI study in its urban slums. Methods: Validity and reliability of the CHERG VASA-tool were tested using face, content, discriminant validation and reliability tests on one hundred randomly selected mothers, with a recent child death event. Data were computed on SPSS (version-21) and R. Results: Testing yielded high I-CVI (>81.43%); high Cronbach's Alpha (0.843); accuracy of between 75% and 100% of the discriminants classifying births to live and stillbirths. The tool showed ICVI (>82.07% and 88.98% respectively) with high accuracy (92% and 97% respectively) for assigning biological and social causes of child deaths respectively. Conclusion: The CHERG VASA questionnaire is valid, reliable, and relevant to the conceptual framework. This valid tool is one of the assets for child health policy as it can assign accurate medical and non-medical causes (pertaining to health-seeking practices) of child mortality cases occurring in Pakistan.