Workplace social capital (WSC) reflects aspects related to social cohesion in the workplace, such as trust, reciprocity and social network that renders it a relevant job resource. In the present chapter, we argue that WSC may mitigate the unfavorable effects of job insecurity on work engagement and in-role performance. A cross-sectional study of 376 employees from various Greek universities was conducted. Contrary to expectations, results showed that qualitative job insecurity was negatively related to work engagement in conditions of higher WSC, while in conditions of lower WSC, the relationship was non-significant. Also, it related positively to in-role performance in conditions of lower WSC and non-significantly in conditions of higher WSC. Post-hoc analyses showed that the social network sub-dimension of WSC was mainly responsible for these unexpected moderating effects. Regarding work engagement, results suggest that higher WSC under insecure conditions may impair employees’ motivation. Also, excessive social exchange, as reflected in higher WSC, may indicate a lack of resources when employees are not positioned at the center of the network and cannot take advantage of it. For job performance, results imply that in insecure jobs, employees may pressure themselves to reach performance goals when WSC is lacking and cannot function as a safety net.