This paper develops a Stackelberg game model for a retailer-led secondary low-carbon supply chain (L-CSC) comprising a manufacturer and a retailer. Then, a two-part pricing contract is designed to investigate the product pricing, carbon reduction, and sales effort decision problems, and relevant management insights are obtained through numerical analysis. The study shows an efficiency loss in decentralized decision making compared to centralized decision making. Considering the sales effort improves the efficiency of the supply chain, retail price, carbon emission reduction (CER), sales effort level, and supply chain profit positively relate to product low carbon preference and sales sensitivity coefficients. The designed two-part pricing contract can increase the profit of the entire L-CSC and optimize the decision level under centralized decision making.