While the doctorate was once perceived as preparation for an academic position, internationally more than half of all graduates leave the higher education sector by choice or lack of opportunity. We know little of how they perceive and navigate the transition from PhD to other career. This longitudinal study of 23 sciences doctoral students, post-PhD researchers, and pre-tenure academics in Canada assessed the interpretive value of two constructs in explaining changes in career thinking and decision-making. The interaction of horizons for action (personal influences on future intentions), and opportunity structures (knowledge of career opportunities) provided a means to explain individual shifts over time and differences across roles in career thinking. Generally, over time and across roles, their knowledge of career opportunities grew, but concurrently their personal horizons for action became narrower due to changing personal relationships and responsibilities. Both the significance of the findings and the pedagogical implications are explored.