This article shares lessons learned from using Opinion Leader Research (OLR), used here as an advocacy tool to strengthen policymaking for MIYCN. In five Southeast Asian countries - Cambodia, Laos, Indonesia, Timor-Leste, and Thailand - OLR was used to gather information on barriers and solutions to guide strategic engagement for MIYCN policymaking, helping to identify influential leaders and opportunities. The authors recommend using OLR in the future as a strategic activity to both inform and generate support for MIYCN policy making processes.