Cities are responsible for about three quarters of global greenhouse gas (GHG) emissions. The overall aims of this research were to quantify citywide GHG emissions and explore the feasibility of mitigation options and their contribution toward supporting Thailand’s Nationally Determined Contributions (NDC) and the 1.5 °C limit pathway. The results obtained using the Global Protocol for Community-Scale GHG emission inventories, revealed that Bangkok emitted 41,965,809 tons of CO₂eq (7.39 tCO₂eq per capita). The stationary energy sector was the largest source (60%), followed by the transportation and waste sectors. Electricity consumption in commercial buildings was the main source of emissions in Bangkok’s stationary energy sector. GHG emissions are projected to dramatically increase by up to 63% from 2015 to 2050. On-road transportation will be the largest source of emissions in 2050, followed by energy consumption in commercial and residential buildings. By deploying Thailand’s NDC with an emissions reduction of 40%, Bangkok is expected to reduce its emissions by 23 MtCO₂eq lower than the projected Business-as-Usual (BAU) level in the year 2030, emitting only 89.5 MtCO₂eq in 2050. Under the 1.5 °C climate goal scenario, Bangkok should limit GHG emissions to 5.64 MtCO₂eq by 2050 (a 94.98% reduction compared to the BAU emission level). To reach net-zero emissions by 2050, all sectors in Bangkok would need to fall significantly. Commercial buildings and on-road transportation were shown to have the largest reduction potential. Regarding the marginal abatement cost (MAC) curve analysis, climate mitigation measures with cost-effectiveness ranging from –658 to 1523 $/tCO₂eq could reduce GHGs by 106 MtCO₂eq toward the 1.5 °C pathway. Replacing appliances with ENERGYSTAR certified ones in residential and commercial buildings was considered the most cost-effective measure (− 658 to − 550 $/tCO₂eq). In the transport sector, promotion of electric vehicles showed the highest cost-effectiveness (1523 $/tCO₂eq), followed by phasing out of old vehicles (421 $/tCO₂eq), and expanding the routes of the Bangkok Mass Transit System (− 65$/tCO₂eq).