Although principal investigators (PIs) are becoming key strategic actors in shaping new scientific trajectories, little is known about how they strategise in an evolving publicly-funded research environment. Drawing on thirty interviews and extensive documentation from Ireland's science, engineering and technology (SET) sector, we take a closer look at the heretofore neglected strategic behaviours underlying the research activities of PIs. Our findings suggest that their strategic behaviours fall into four categories – research designer, research adapter, research supporter, and research pursuer. We find that the mechanisms for selecting research strategies are interwoven with the posture (reactive/proactive) of PIs as well as their degree of conformance. We argue that more proactive PIs utilising non-conformance strategies shape new research trajectories, while conformative and/or more reactive PIs predominantly pursue and deepen existing trajectories. We discuss the wider implications of these findings for policy makers, funding bodies and the practicing PI and strategist.