Sustainable supply chain management (SSCM hereinafter) plays a significant role in the development of business strategies. Scholars and practitioners have thus devoted their effort to investigating the driving forces of SSCM and measures which serve to enhance its performance. A review of extant literature indicates that previous studies have focused on internal and external pressures as the main drivers of SSCM, while the crucial role of the diversity of the supply chain alliance system has not received sufficient attention. In view of such a literature gap, this research aims to explore the contribution of alliance portfolio diversity in sustainable supply chain practices and its impact on SSCM performance. Relevant diversity-related theories are applied to explain the mechanisms of alliance portfolio diversity and their effect on SSCM performance through several mediating roles. Furthermore, the current research framework is tested within contingencies, thereby providing better insight into the studied subject matter. A field study is conducted to examine the proposed framework and related hypotheses wherein survey data comprised from the participation of more than 300 manufacturing firms are collected and tested. An analysis of the findings confirms the significant role of alliance portfolio diversity in SSCM performance, in particular under contingencies. As a result of such findings, this current research not only provides field evidence for the applicability of applied theories, but also draws a set of theoretically grounded guidance criteria into SSCM policies for field practitioners to enhance supply chain performance within the scope of sustainability.