The escalating complexity of supply networks is undeniable, and organizations grapple with myriad globally dispersed suppliers spanning diverse industries and operating amid volatility and uncertainty while having multifaceted interactions. In line with this, scholars have been investigating supply network complexity (SNC) for over two decades, yet the domain is not converging; definitions and operationalizations are varied, a multiplicity of theoretical perspectives exists, performance implications are inconclusive, and supply chain managers are certainly still struggling with the complexity of their supply networks. To address this critical gap, we conducted a rigorous systematic review of 116 articles and synthesized the extant research in a comprehensive nomological network of SNC. Our synthesis encompasses the following key aspects: (i) defining (sub)dimensions of SNC by reconciling diverse conceptualizations, (ii) elaborating on the direct and contingent effects of SNC by highlighting underlying mechanisms and relevant theories, (iii) identifying antecedents of SNC, and (iv) introducing a detailed categorization of SNC management practices and illustrating SNC management capability as an antecedent of such practices. We conclude by presenting an extensive research agenda illustrating the gaps in the literature and charting a path forward in relation to different themes, theories, and methods.