Cantilever retaining walls are prone to corrosion damage, particularly the reinforcement bars along the horizontal construction joint, raising concerns about structural integrity. Traditional inspection methods, often limited to visual assessments and invasive core sampling, provide limited information for accurate condition assessment. This paper introduces a novel non-destructive inspection method for evaluating the corrosion state of reinforcement in these walls. A pilot application on a 50-year-old wall in Switzerland demonstrated the method’s feasibility and accuracy. The analysis of half-cell potential and electrical resistance measurements revealed varying levels of corrosion risk along the wall, which were confirmed through destructive inspections of three shafts. The destructive investigation established a strong correlation between the mapped corrosion risk and the observed reinforcement damage with a cross-sectional loss of 25% in areas with high risk. This inspection method offers several advantages over traditional methods, including comprehensive coverage over the length of the retaining wall, reduced invasiveness, and the potential for automated data acquisition. The findings highlight this method’s potential for enhancing the accuracy and efficiency of corrosion assessment in cantilever retaining walls, enabling proactive maintenance and extending their service life.