External involvement in new product development (NPD) has received increasing attention from both academicians and practitioners in recent years. While external involvement has been studied extensively, the academic understanding on how external involvement influences firm performance and the role of time-to-market of new products is still very limited. Drawing on the literature on innovation search and knowledge-based view, we develop a conceptual framework in which external involvement is linked to time-to-market of new products and firm performance. We tested this model using data collected from 176 manufacturing companies in China. The results indicate that both customer and supplier involvement can contribute to the reduction of time-to-market of new products. We also show that time-to-market of new products completely mediates the relationships between two types of external involvement and two dimensions of firm performance. These findings have important implications for research and practice in both the external involvement and the NPD areas.