ABSTRACT Following the Snowden revelations, Cambridge Analytica, and a policy vacuum created by technological convergence and neoliberal reforms, policy efforts to articulate oversight of digital platform markets gathered policymaker support and public attention internationally. In the U.S., examined here as a case study of these international policy efforts, competition policy emerged as a prominent governance mechanism over digital platforms, resulting in the current antitrust scrutiny of tech giants like Google and Meta. Drawing on policy documents, fieldwork, and expert interviews, I trace how antitrust reform proposals, pitched as reclaiming democratic governance over private markets, came to dominate platform policy discussions. I examine how policy efforts to address platform power via competition grappled with non-competitive harms arising in digital markets, such as threats to user privacy and disinformation flows. Finally, I show how these debates began to converge on the contours of an emergent governance paradigm for digital platform oversight. I argue that this governance framework, which seeks to optimize market mechanisms to discipline platform markets, has significant limitations, notably in addressing issues associated with big data commodification and quantification.