Academics are increasingly encouraged to acquire external grants to finance their research, and often hold grants from multiple funders concurrently to ensure the continuity of their work. However, there are concerns that inefficiencies occur when funding is received from multiple sponsors, especially when this originates from different sectors. This study investigates complementarities between public/non-profit and private sector sources of research funding with regard to academic output in terms of publications, research impact and research orientation. The empirical analysis is based on novel data on external public/non-profit research grants and industry funding for tenured engineering academics employed at fifteen UK universities. The results suggest that while research grants are generally associated with higher research outcomes, industry funding decreases the marginal utility of public/non-profit funding by lowering the increase in publication rate associated with public/non-profit grants. At the same time, for more commercially oriented research, measured as its patentability score, we find some support for complementarities between public and private-sector research funding. These results suggest that provision of public grants is crucial to the production of research that is distributed openly through publications and proceedings. Private sector grants are important as they may enable more applied research trajectories for those capable of combining publicly and industry sponsored research.