The drawbacks in the service operations of the Indian public sector banks include high cost per employee and lower service quality compared to private and foreign banks. This article for the first time confirms the application of lean thinking for process improvement of service operations in an Indian public sector bank through ‘value stream mapping’. The article uses action research methodology and two case studies that describe the process and outcomes of the action research to achieve the objective of studying the applicability of lean thinking and lean tools in process improvement of bank branches. The results of introducing lean thinking in the branches of the public sector bank in India were efficiency improvements through lower wait time for customers and lower stress levels for employees, besides increased customer satisfaction, profit and business—factors which justify and support the use of lean thinking in banks.