Entrepreneurial passion is socially contagious. However, do entrepreneurs also select whom they interact with based on passion similarity? The complex interdependencies between social networks and entrepreneurial passion remain undertheorized and empirically puzzling. Using a stochastic actor-oriented model (SIENA) and four waves of panel data, we test hypotheses about the co-evolution of social networks and entrepreneurial passion during a 5-month startup accelerator program. We observe that social ties occur more frequently among peer entrepreneurs who are similar in levels of passion for founding. Initial homophily selection explains 34% of this observed similarity whereas social contagion explains 57%. Finally, we find that passion for founding is more contagious among members of startup teams than across other peer ties. Surprisingly, none of these effects are significant for passion for inventing. We discuss the theoretical and practical implications of these findings. •We disentangle homophily selection and social contagion of entrepreneurial passion within a startup accelerator cohort.•Entrepreneurs form ties with peers who share their passion for founding.•Passion for founding is contagious among network ties.•No selection or contagion effects found for passion for inventing.•Our study offers a comprehensive view of how entrepreneurial passion and social networks coevolve.