In this study, energy, exergy, and environmental (3E) assessments have been conducted on a proposed combined-cycle power plant (CCPP) with three pressure levels of the HRSG and reheating process. 3E design approaches cross-link mechano-electric and environmental objectives. Herewith, the suggested combined-cycle is formed by a gas unit, condenser, steam turbines, triple-pressure heat recovery steam generator (HRSG) and also utilizes reheat facilities and auxiliary components. It is observed that more than 56% of total exergy destruction occurs in the combustor, followed by HRSG (15.29%), steam turbines (roughly 15.02%), gas turbine (8.93%), air compressor (1.79%), and condenser (0.66%). A parametric study is also presented that examines the sensitivity of performance indicators to various environmental states, steam pressures, pinch points, and steam mass flow rates. Moreover, it is presented that the implementation of Siemens SGT-100-1S over other GT configurations can considerably reduce deficiency of the overall cycle. The effects of each contaminant mass flowrate (NOx, CO, UHC, and CO2) and adiabatic flame temperature (AFT) are also studied when the gas unit operates under partial power and incomplete combustion conditions. In conclusion, a number of potential causes of irreversibilities and corrective optimization guidance are offered for each main equipment of the CCPP.