Knowledge sharing (KS) behavior is one of the main drivers to generate social sustainability. It predicts high organizational performance and innovation capabilities, and creates enjoyment and happiness in helping others. Even if incentives to enhance KS behaviors exist, employees would still be reluctant to share knowledge. For this reason, we test a comprehensive model of sustainable human resource management with the inclusion of KS to explain how to enhance collaborative practices in terms of voluntary knowledge sharing. In a comprehensive model, we incorporate organizational justice, employee perceived organizational support, job satisfaction and affective organizational commitment, and how they relate in order to generate knowledge sharing behavior. Using a sample of 1350 employees working for multinational firms operating in Spain, the present research obtains two main results. First, organizational justice, employee perceived organizational support and affective organizational commitment are positively related with KS. Second, employee perceived organizational support, job satisfaction and affective organizational commitment play a mediating role between organizational justice and KS, which reinforces the positive relationship between both constructs. Consequently, employees would be more willing to cooperate and share in fair organizational contexts, especially when they are satisfied and affectively committed, and when their contributions are valued and recognized. Finally, we discuss human resource management’s (HRM) practical interventions and recommendations for future research on sustainable organizations.