Due to workers’ vulnerability in construction sites, workplace safety has become of particular interest, and the current literature offers myriad approaches to dealing with it. From a social and organizational lens, this study explores an empirical model that integrates the dimensions of social capital theory (SCT) and leader-member exchange (LMX) in modelling the safety behavior of construction workers, particularly relevant in small-medium construction firms. The data were collected from 232 construction workers in the central Philippines. The responses were analyzed using partial least squares—structural equation modeling to investigate five hypothesized paths, including the influence of SCT dimensions (e.g., structural, relational, and cognitive) on LMX and LMX on safety behaviors (i.e., compliance and participation). We also tested whether the relationship of LMX to safety behaviors is moderated by age. The results indicate that the three dimensions of SCT have a significant and direct influence on LMX. In addition, LMX directly affects safety participation but does not significantly affect safety compliance. Particularly in small and medium construction firms with relatively flat organizational structures and supervisors displaying diverse roles, these findings suggest that the social relationships of workers tend to promote their trust and professional respect for supervisors who can leverage their position to encourage them participate in safety initiatives. On the other hand, age negatively influences the relationship of LMX to safety participation, indicating that younger workers tend to better translate high quality LMX into initiatives that promote overall workplace safety. Our findings offer the first evidence of the positive relationship between SCT and LMX in advancing the safety participation of construction workers. From these insights, practical inputs to the design of relevant measures and future research works are outlined.