Most theoretical frameworks in entrepreneurship emphasize that entrepreneurial passion drives entrepreneurial effort. We hypothesize that the reverse effect is also true and investigate changes in passion as an outcome of effort. Based on theories of self-regulation and self-perception, we hypothesize that making new venture progress and free choice are two factors that help to explain why and under which conditions entrepreneurial effort affects entrepreneurial passion. We conducted two studies to investigate our hypotheses. We conducted a weekly field study with 54 entrepreneurs who reported entrepreneurial effort and passion over eight weeks (341 observations). The results showed that entrepreneurial effort predicted changes in entrepreneurial passion. We conducted an experiment (N = 136) to investigate the effect of effort on passion and the underlying psychological processes in a laboratory setting. The results revealed that new venture progress mediated the effect of entrepreneurial effort on passion and that free choice moderated the mediated effect. Overall, our findings provide a new theoretical perspective on the relationship between entrepreneurial effort and passion.