This paper explores the energy management of a natural gas-based thermal power plant, with a focus on improving its efficiency, sustainability, and economic feasibility. The study uses the Ashuganj Power Station Company Limited (APSCL) in Bangladesh as a case study. To evaluate the efficiency of the APSCL, both energy and exergy perspectives are considered, and sustainability is assessed through exergetic parameters. The plant’s economic feasibility is analyzed based on its fuel costs and operational losses. The results of the study indicate that the energy and exergy efficiencies of the APSCL vary from 32.97% to 33.21% and from 32.63% to 32.87%, respectively, for steam turbines and from 39.77% to 56.98% and from 39.36% to 56.40%, respectively, for combined cycle power plants (CCPP) during 2016–2021. The slightly lower efficiency in exergy calculations accounts for the system loss incurred over time, which is often omitted in efficiency calculations using energy parameters. To measure the sustainability of the APSCL, eight key indicators are used: the depletion number, exergy sustainable index, cumulative exergy loss, relative irreversibility, lack of production, the wasted exergy ratio, environmental effect factor, and improvement potential. The results indicate that APSCL still has opportunities for improvement in terms of sustainability, with 50% of the fuel being depleted in the plant, contributing to a sustainable index of 2.00 and cumulative exergy loss varying between 48.59 and 21.17. Regarding financial costs and losses, APSCL has experienced an increasing trend in the price of electricity generated. However, by implementing intelligent maintenance practices and upgrading equipment in a timely manner, it is possible to minimize costs and increase exergy output, reducing the per-unit fuel requirement for electricity production and the global carbon footprint significantly.