To understand the intermediary role of accelerators in the developing regional entrepreneurial ecosystem of Bangalore, we analyze data from 54 interviews with accelerator graduates, accelerator managers, and other ecosystem stakeholders and from 49 websites, 13 online video interviews, 26 online news sources, and 301 pages of policy documents. Specifically, we adopt a socially situated entrepreneurial cognition approach to theorize how accelerator expertise, existing at a meso‐level, intermediates between (micro‐level) founders and the (macro‐level) ecosystem. In our model, four types of accelerator expertise—connection, development, coordination, and selection—together increase stakeholders’ commitment to the entrepreneurial ecosystem, leading to venture validation (success or failure) and ecosystem additionality. These findings indicate that accelerators contribute to ecosystems in a way that is distinct from, but supportive of, building individual ventures.