Fine particulate matter (PM2.5) pollution remains a major environmental and public health challenge across the Indo Gangetic Plain (IGP), one of the most densely populated and polluted regions in the world. Uttar Pradesh (UP), the most populous state in India, experiences persistently high PM2.5 concentrations due to emissions from residential energy use, industry, transport, agriculture, and regional transport of pollutants. Despite recent policy initiatives such as the National Clean Air Programme, many urban and rural areas in the state continue to exceed National Ambient Air Quality Standards (NAAQS). This study evaluates cost-effective mitigation strategies for improving air quality in UP using the GAINS (Greenhouse gas–Air pollution Interactions and Synergies) model adapted for the IGP region. The analysis develops a region-specific emission inventory for UP for the baseline year 2020 and assesses future air quality outcomes to 2035 under current legislation and enhanced mitigation scenarios. The results show that in the base year 2020, approximately 44% of population-weighted PM2.5 exposure in UP originates from sources outside the state, highlighting the importance of regional pollution transport. Secondary particulate formation contributes about 40% of total ambient PM2.5 concentrations. Under the current policies, PM2.5 exposure in 2035 remains well above national standards. Additional mitigation measures across residential, industrial, transport, and agricultural sectors can substantially reduce exposure levels at relatively low cost. The findings highlight the need for coordinated emission reductions across the IGP region and provide a basis for prioritizing cost-effective air quality interventions in UP.