Buying firms collaborate with suppliers in New Product Development (NPD) to better leverage their resources and knowledge. Prior studies' results on IT contribution to NPD project performance are mixed, and none investigated this effect for collaborative buyer-supplier NPD projects. This study adopts a contextual functional approach to explore how the effective use of IT functionalities for the three classical IT-enabled NPD activities, namely Project and Process Management (PRM), Knowledge Management (KM), and Cooperative Work (CW), impacts NPD project success in terms of project performance but also regarding the contextual factor of collaboration quality. A series of multiple linear regressions is performed to test these effects using data from a survey with 90 firms involved in collaborative NPD projects with suppliers. As results, the effective use of all IT functionalities directly improves collaboration quality, while only KM directly affects project performance. PRM and CW contribute to this performance only indirectly through collaboration quality. Hence, this study emphasizes the importance of considering a functional approach when studying the impact of IT effective use on NPD project success, and of taking into account the project context. Additionally, it incites practitioners to build a conducive collaboration climate to benefit from using IT functionalities.