Most individuals vulnerable to depression do not receive adequate or timely treatment globally. Unguided computerized cognitive behavioral therapy (cCBT) has the potential to bridge this treatment gap. However, the real-world effectiveness of unguided cCBT interventions, particularly in low- and middle-income countries (LMICs), remains inconclusive. In this study, we report the design and development of a new unguided cCBT intervention, TreadWill, and its pragmatic evaluation. TreadWill was designed to be fully automated, engaging, easy to use, and accessible in LMICs. To evaluate its effectiveness and engagement level, we performed a double-blind, fully-remote, randomized controlled trial with 598 participants in India. The use of TreadWill significantly reduced depression-related and anxiety-related symptoms. Compared with a plain-text version with the same therapeutic content, the full-featured version of TreadWill showed significantly higher engagement. Overall, our study provides a new resource and evidence for the use of unguided cCBT as a scalable intervention in LMICs.