Volunteering, STEM education and occupation, and information-processing skills such as literacy, numeracy, and digital problem-solving skills are important indicators of a nation’s well-being as they represent civic engagement, economic development, and the human capital of the population. Although these critical social indicators have been previously examined in silos, the interrelationships are yet to be examined in the adult populations in the United States. The current study analyzed the 2012/2014/2017 U.S. Program for the International Assessment of Adult Competencies (PIAAC) data of adults aged between 25 and 65 years old (n = 8,330). Results from the structural equation model showed that STEM education and occupation as well as information-processing skills independently promote volunteer participation. Also, STEM education and occupation are positively associated with information-processing skills. Yet, when simultaneously examining the mediation relationship, STEM education and occupation are no longer the promoters of volunteering. Findings from the current study can provide preliminary education, labor, and social policy implications for promoting the nation’s economy and well-being, and inform future research to disentangle complex interrelationships across the important social indicators.