Universities are becoming more closely associated with communities, with many embracing a third mission as part of their recognized mission of sustainable development. Since holistic indicators are essential to measuring the post-intervention social impact of university–community engagement programs toward sustainable development, this study developed and validated a comprehensive set of sustainability indicators that would help universities conduct a meaningful measurement of social impact. Using a structured questionnaire, data were collected from 310 professionals and stakeholders in the Khanab Nak community in the Pak Phanang River Basin, Nakhon Si Thammarat Province, Thailand. The collected data were analyzed using a five-stage process, including data reliability and validity, descriptive statistics, differences in group opinions, principal component analysis, model testing, and confirmatory factor analysis for fit statistics. As a result, 15 indicators were identified after synthesizing the common indicators from the sustainable development goals. The indicators were divided into three groups using exploratory factor analysis. Confirmatory factor analysis supported these findings with model fit indices, construct validity, and high reliability, as demonstrated below, i.e., social challenges, economic growth, and sustainable living. The practical implementation of the study’s findings could broaden the perspective of universities on promoting sustainable development goals and incorporating them into strategic plans to build capacity for scaling up engagement activities for community development.