Vanadia (V₂O₅)- and manganese (MnO_x)-based catalysts are widely used in the selective catalytic reduction (SCR) process for NO_x removal from various sources, particularly in diesel engines. Extensive research has been carried out to modify the traditional V₂O₅- and MnO_x-based SCR catalysts to overwhelm their disadvantages such as low thermal stability, ammonia slip and insufficient Hg⁰ oxidation. This review focuses on the advancement in the modification of V₂O₅- and MnO_x-based SCR catalysts in different aspects like increasing thermal stability, oxidizing slip ammonia, reducing SO₂ oxidation, improving Hg⁰ oxidation efficiency, enhancing N₂ selectivity and expanding the operation temperature window. The performances of various V₂O₅- and MnO_x-based SCR catalysts have been examined in detail and also categorized based on materials such as transition metals, rare earth metals, noble metals and others. According to the previous studies and researcher's perspective, it was noticed that doping of suitable components promotes the overall performance of V₂O₅- and MnO_x-based SCR catalysts. The incorporation of transition metals into V₂O₅- and MnO_x-based catalytic systems has shown a vast potential to control various pollutants in the exhaust gas after-treatment techniques.