The influence of temperature (25, 75, and 150 °C) on the passivation behavior of Modified Martensitic 13Cr Stainless Steel (M13Cr) in CO₂ saturated acidic salt brine environments was investigated. The material was found to contain Ti(C,N) inclusions and Volta potential maps obtained through scanning Kelvin probe force microscopy (SKPFM) identified them to be more anodic (60 mV lower) than the matrix. Cyclic polarization (CP) showed a shift in pitting and repassivation potentials to more negative values at higher temperatures. Electrochemical impedance spectroscopy (EIS) and Mott–Schottky tests showed that the passive film formed was more defective with increasing temperature. X-ray photoelectron spectroscopy (XPS) confirmed the presence of a defective passive film with reduced repassivation capabilities due to higher contents of soluble CrO₃/Cr⁶⁺ species at temperatures exceeding 75 °C. These results offer valuable insights into understanding the pit initiation mechanisms and performance of M13Cr.