In this study, we investigated a closed-loop supply chain system comprising manufacturers and retailers engaged in recycling competition. The manufacturer is the CLSC Stackelberg leader. By developing a Stackelberg model incorporating marketing, we analyzed the impact of marketing efforts by different agents on the entire system, specifically focusing on marketing conducted by the manufacturer, the retailer, and the centralized supply chain. Our findings reveal that the manufacturer consistently prefers the retailer to undertake marketing efforts. In contrast, the retailer favors the manufacturer to handle marketing when recycling competition intensity is low but prefers to conduct marketing themselves when the competition intensity is high. The extent of environmental harm under different models depends on the base demand: no marketing results in the least harm when the base demand is low, marketing by manufacturers minimizes harm when the base demand is moderate, and marketing by retailers causes the least harm when the base demand is high. Then, we performed a numerical analysis of the marketing cost-sharing contract and found that an appropriate sharing ratio consistently enhances the profitability of the entire supply chain. Finally, we examined the impact of a government subsidy for remanufacturing on supply chain performance and found that when recycling competition intensity is moderate, a government subsidy enhances supply chain performance more effectively.