The application of thin-film composite mixed-matrix membranes (TFC-MMMs) for gas separation is widely considered as an efficient separation technology. The principal methods for the preparation of TFC-MMMs are dip-coating, phase inversion, and interfacial polymerization comprising different types of support layers. These methods influence the CO2 permeation over the selective and support layers. A comprehensive review is provided for capturing new details of progress achieved in developing TFC-MMMs with detailed performance of gas separation in the previous few years. Various preparation techniques of TFC-MMMs and their effect on the gas separation performance of the prepared membranes are described.