Entrepreneurship research on prosocial motivation has outlined its positive impact on well-being, but still little is known about its power, which may have deleterious personal consequences under certain conditions. In this study, we ask whether prosocial motivation can harm entrepreneurs' subjective well-being when they run a commercial venture. Embedded within a contingency perspective informed by self-determination theory, we build on longitudinal survey data to explain the effect of prosocial motivation on entrepreneurs' overall life satisfaction. Our analysis demonstrates that prosocial motivation has a negative effect on entrepreneurs' life satisfaction due to increased levels of stress. However, our findings show that the negative effect of prosocial motivation dissipates when perceived autonomy at work is high compared to when it is low. Overall, our research raises questions on the role of prosocial motivation for entrepreneurs' subjective well-being and, in particular, discusses its potential “dark side” in the context of commercial entrepreneurship. Executive summaryCan there be a “dark side” in helping others? If so, how can we better understand under what conditions it emerges? Entrepreneurship research conventionally presents prosocial motivation as a positive driver for social venture creation and entrepreneurs' well-being. However, we have little knowledge about the consequences of prosocial motivation when we move outside the social entrepreneurship context. When prosocially motivated entrepreneurs lead a commercial venture, they face the difficult task of balancing the desire to help others with the financial requirements of the business. The challenge of simultaneously accomplishing commercial and prosocial goals can result in a stressful experience that is detrimental to the entrepreneur's well-being. In this study, we ask whether and under what circumstances prosocial motivation can harm entrepreneurs' well-being.Embedded in a contingency perspective informed by self-determination theory, this article expands our knowledge on the effects of prosocial motivation in the context of commercial entrepreneurship. We draw from original longitudinal survey data on 186 entrepreneurs in the United Kingdom to demonstrate that prosocial motivation causes entrepreneurs stress and through that stress has a negative effect on their life satisfaction. We also show that the negative effect of prosocial motivation diminishes when the degree of autonomy entrepreneurs perceive in the pursuit of daily work tasks is high. To explore the uniqueness of the entrepreneurial context, we run a comparative analysis with a sample of 544 employees. This analysis confirms that stress fully mediates the negative relationship between prosocial motivation and subjective well-being, but for employees, this negative effect disappears when their level of intrinsic motivation—the desire to expend effort based on enjoyment of the work itself—is high.Building on our findings, we generate several important contributions. First, we help develop an understanding of the “dark side” of prosocial motivation by demonstrating that under certain circumstances, the desire to help others can be detrimental to entrepreneurs' subjective well-being. Second, we expand knowledge about the link between prosocial motivation and well-being by considering the boundary conditions (perceived autonomy and intrinsic motivation) that influence the dynamics of their relationship. Third, we set the stage for further investigations that aim to clarify the relationship between motivation and perceived autonomy and its effect on personal outcomes across different work domains.The key insight of the study is that prosocial motivation creates a dilemma for entrepreneurs when operating a commercial business such that the desire to help others outside the context of immediate work tasks can harm their personal well-being. We also find that the perception of autonomy is key for commercial entrepreneurs to be able to realize their prosocial motivation without creating stressful situations. Extending our understanding of the conditions that shape the relationship between prosocial motivation and well-being among entrepreneurs would help in developing a more holistic notion of prosocial business venturing, one that includes the role of both commercial and social enterprising activities in contributing to personal and societal well-being.