The paper aimed to investigate and evaluate the performance of natural aqueous cornflower (Centaurea cyanus) extract (CFE) to mitigate carbon steel corrosion in harsh saline formation water. Weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques were all used for this assessment. The polarization results showed that CFE could act as a mixed-type inhibitor with a reasonable protection efficiency of similar to 69% at very low extract addition of 10 ppm. CFE retained its inhibitive effect even at elevated temperatures where it showed an inhibition efficiency of 63.95% at 313 K. The adsorption behavior of the main CFE constituents on carbon steel surface was well described following Langmuir adsorption isotherm. Thermodynamic activation parameters that govern carbon steel corrosion in blank and extract-containing saline formation water were calculated from the temperature dependence and then discussed. The effect of immersion time on the weight loss rate indicated that CFE not only keeps its inhibitive activity for carbon steel in saline water, but also improves its effectiveness over the long term immersion due to synergistic influence of the corrosion products which offer an additional protection. Structural characterization by using SEM-EDX images and FT-IR analysis further supported the obtained chemical and electrochemical results.