Innovation and design literature have given limited consideration to the strategic role of design consultancies in the innovation processes of their clients. A plausible explanation is the difficulty to assess the quality of design consultancies’ output, given the intangibility of the output itself and the difficulty of connecting a knowledge-intensive output to clients’ performance indicators. In this paper we examine design consultancies’ impact on their clients’ strategic decision-making as a way of capturing design consultancies’ strategic role in their clients’ innovation efforts. Design consultancies can influence strategic decisions by enhancing three strategic decision-making mechanisms identified by the literature – rationality, intuition, and political behaviour. By examining the Dutch design consultancy industry, we find initial evidence of design consultancies’ capability of affecting clients’ strategic decision-making. Early involvement in problem definition and long term relationships with clients strengthen design consultancies’ influence.