Sustainability standards verify that goods and services meet minimum social and environmental norms. They have rapidly gained traction in value chains that connect lead firms with dispersed global suppliers. Historically, such standards have been created by firms, civil society and state regulators in the global North to govern global value chains sourcing goods and services from Southern producers. However, this century has witnessed the emergence of Southern-led sustainability standards. This study addresses research gaps around how Southern standards are shaped by public and private actors, or how domestic as well as global value chain dynamics impact their development. This is done through a comparative study of Chinese clothing and Indian tea standards. Drawing upon the concepts of synergistic and antagonistic forms of governance, this report analyses how, when and why Southern actors (public, private and social) choose to develop new sustainability programmes which either emulate or disrupt established transnational standards within this governance arena. Recognising the agency of Southern actors, but also their constraints to act within this established field, this paper examines how the sector-specific political economy dynamics of apparel and tea production shape the mechanisms, processes and relations through which Southern sustainability standards are forged in this increasingly multi-polar world of trade and production.