In this article, hydrothermal flames were studied and an extended flamelet model was developed accounting for the real-fluid effects. The newly formulated real-fluid flamelet/progress variable (FPV) model was evaluated in a laminar counterflow configuration through both a priori and a posteriori analyses. At supercritical conditions, the ideal-gas model results showed a higher flame temperature and intermediate species mass fractions compared to the real-fluid model results in both the detailed chemistry (DC) and FPV approaches. To thoroughly evaluate the real-fluid flamelet library, the a priori tests were carried out under atmospheric and supercritical conditions with different strain rates. The comparisons of tabulated quantities and reference values from DC simulations showed that the real-fluid FPV model can correctly predict the thermal properties and species mass fractions in hydrothermal flames. Finally, the a posteriori analysis showed overall good agreement between the FPV and DC results, verifying the newly proposed real-fluid FPV approach.