Given the severe global competition and the manufacturing challenges, retaining competitiveness in the textile and apparel (T&A) industries has become crucial for manufacturers. To achieve this, although historically manufacturers have been regarded as mainly production orientated, a number of them have occupied a primary intermediary position by applying the mechanisms of industrial upgrading and instituting new product development (NPD) in their businesses together with the synergy of alliances and networks. This has enabled the manufacturers to provide various products and services to international buyers. The Taiwanese T&A manufacturers can serve as a good example. They have managed to retain their competitiveness in the global industry for the last half century by continuously evolving their businesses and acquiring extensive capabilities. To achieve competitiveness in the T&A sectors, strategic planning that can lead to competitive advantages is required. NPD has emerged as a source of business competitiveness and its success determinants can lead to competitive advantages. Supply management, particularly partnering relationships, is crucial to manufacturers' competitive advantage, since no single firm can possess all the necessary resources and capabilities. Against this background, this study has constructed a research framework, in line with the resource-based view (RBV) and transaction cost theory (TCT), in order to explore how competitive advantages can be achieved, which can lead to manufacturers' competitiveness. An in-depth case study of a representative Taiwanese manufacturer has been employed and examined. The selected Taiwanese T&A manufacturer has acquired resources, various (dynamic) capabilities and knowledge through its NPD process, resulting in core competences and sources for competitive advantages. It has become a lead firm in its supply chain/network, deploying a variety of partnering relationships in order to conduct NPD activities strategically, and has vertically integrated T&A NPD. This has allowed it to provide an increasing variety of new products and services, in order to serve a wider range of customers, thus continuously acquiring business opportunities in dynamic markets. This study has found that the manufacturers in the T&A industries can adopt more proactive strategic modes in NPD activities, to enhance NPD outcomes and their relationships with buyers. It is important for manufacturers to acquire crucial and complementary resources/capabilities through strategic networks, developing alliances to strategically plan and implement NPD. Operational relationships need not only to be viewed in relation to their immediate cost reduction benefits, but also to be extended to longer-term collaborations, in order to achieve competitive advantage deriving from evolving products and cost benefits based on a holistic and strategic view of the business.