<p>This article explores the dynamics of a dual-channel green supply chain that offers manufacturers a strategic advantage by balancing direct sales and third-party (TP) e-commerce (EC) partnerships under government eco-label regulation. We develop two decentralized models – one with a manufacturer-owned online channel and another with an e-commerce-led channel – employing a manufacturer-led Stackelberg game to assess the performance implications of these sales strategies. Additionally, we propose a composite two-part tariff contract to enhance channel efficiency and address coordination issues. The findings indicate that: (<i>i</i>) manufacturer-owned online channels enhance overall efficiency, whereas excessive commission fees in TP channels erode profitability significantly; (<i>ii</i>) increased channel competition positively influences overall supply chain performance; (<i>iii</i>) the proposed contract not only fosters win-win-win outcome for channel participants but also boosts overall performance; (<i>iv</i>) sensitivity analysis identifies critical parameters that influence supply chain outcomes, providing valuable guidance for the manufacturer navigating the complexities of eco-labeling and market competition. This research contributes to the sustainable supply chain management by offering guidance on eco-label standards, subsidy levels, and contractual arrangements that align manufacturer and retailer interests, thereby promoting a more competitive and environmentally friendly marketplace.</p>