Gravity data retrieved from the Bureau Gravimétrique International and the Gravimetric Atlas of Switzerland have been used to evaluate their applicability as a subsurface investigation tool to assess key geological features in support of the geothermal exploration in the Geneva Basin (GB). In this context, the application of an effective processing workflow able to produce reliable residual gravity anomalies was implemented as a crucial first step to investigate whether and to what level gravity anomalies can be correlated to geologic sources of geothermal interest. This study focusses on the processing workflow applied to publicly available gravity data, including the quantification of the uncertainty. This was then also used for first-order 2D forward gravity modelling. The resulting residual anomalies demonstrate the potential use of gravity investigations for geothermal exploration in sedimentary basins, and also reveal areas of significant, irreparable misfit, which calls for the use of complementary data and 3D subsurface structural knowledge. The results of such investigations will be presented in subsequent studies.