Social impact investors claim to promote sustainable development by mobilizing private finance capital to solve pressing global challenges like poverty alleviation. In this paper, I interrogate this claim through an examination of microfinance in Cambodia, a major destination for impact investment. In the past decade, Cambodia has received nearly 10% of global investments from microfinance-specific funds. It now has the largest microfinance-debt per capita ratio of any country in the world. Based on qualitative research between 2021 and 2023, I argue that impact investment functions as an anti-politics of development that reinforces finance as a political technology of neoliberal governance. Over the past two decades, impact investors have poured capital into the country’s microfinance industry to expand access to credit without acknowledging structural political-economic conditions that have produced rising over-indebtedness among microfinance borrowers. Instead, they have argued that the problems created by the microfinance industry are best resolved through a self-regulation model that uses a voluntary code of conduct based on global standards of responsible finance. Thus, impact investors have been integral in broader transformations that have extended financial logics, technologies and accumulation imperatives into people’s daily lives. This paper contributes to economic geography and critical development studies by explaining how impact investment deepens neoliberal financialization.