The conventional bathymetry survey uses a single beam echo sounder (SBES) and multi-beam echo sounder (MBES). However, this technique is challenging to map large ocean areas due to complexity, cost, and time-consuming. This study aims to estimate the multi-mission satellite altimetry bathymetry across the Malaysian Seas. Six satellite altimeter missions with 11 years of data have been utilised to derive mean sea surface height (MSSH). The Gravity-Geologic Method, a conventional terrain inversion method based on gravity data, is employed in this study to estimate bathymetry using a density contrast of 1.67 g cm^-3. The gravity-Geologic method utilises gravity effects to be converted into bathymetry by using an inversion process. The density contrast between the bedrock and the seawater influences the predicted bathymetry. Regional gravity was removed from the observed gravity in order to determine the short-wavelength gravity effects by using the control depths from the shipborne measurements. The findings were validated and compared with shipborne bathymetry data from the National Geophysical Data Centre (NGDC) and Global Bathymetry Models. The estimated bathymetry correlation analysis, R, showed the highest values recorded with 0.9942. These findings reveal that the estimated bathymetry using the Gravity-Geologic Method seems to improve the accuracy of the bathymetry by 69% when compared with the ETOPO1 global bathymetry model. Nonetheless, the estimated bathymetry records 38% improvement when compared to the DTU10 global bathymetry model. The final estimated bathymetry model in this study is known as the UTM18 Bathymetry Model.