As the market has transformed from a producer-centered to a consumer-centered one, corporate competition has become determined more by the introduction of new products than by price competitiveness. With the growing recognition that the development and success of new products critically affect the long-term survival of firms, researchers' attention has been focused on the success factors of new products, among which buyer cooperation has attracted attention as a factor contributing to new product success. However, buyer cooperation in new product development (NPD) projects is not a decision confined to a specific NPD project alone but is a decision influenced by the buyer-supplier relationship within the supply chain; nevertheless, most studies have examined it solely from the perspective of technological innovation. While cooperation between suppliers and buyers has been actively studied as an independent topic not only in the domain of technological innovation through specific NPD project collaboration but also in the domain of supply chain management, studies that simultaneously examine both perspectives are quite scarce. This study collected 176 samples and conducted structural equation modeling analysis and multi-group analysis to elucidate the role of the buyer-supplier relationship, particularly the degree of dependence on the buyer, in the process through which buyer cooperation in NPD leads to new product success. The results confirmed that the degree of dependence on the buyer negatively moderates the effect of buyer cooperation in NPD on performance.