> Technology startups are essential to the global economy. Yet, predicting their short- and long-term outcomes remains difficult. This is particularly true in the early stages of a venture’s lifecycle when little to no performance data are available. We offer large-scale, ecologically valid evidence for the importance of a startup feature that is available from the moment of conception: founder personality. Our findings suggest that while some traits consistently predict startup outcomes across all stages (i.e., emotional stability), others reverse their associations with entrepreneurial outcomes as the startup matures from conception to exit (i.e., conscientiousness). By doing so, they offer novel insights into the role of founder personality in technology startups.