<p>The effectiveness of copper corrosion inhibitors has long been constrained by an insufficient mechanistic insight into the formation of protective films on copper surfaces and their impact on copper corrosion kinetics in chloride-containing media. In this work, the inhibition corrosion kinetics and mechanism of 5-aminobenzothiazole (5-ABT) on copper corrosion in 3.5 wt.% NaCl solution were investigated through a combination of in situ electrochemistry and theoretical calculations. In situ electrochemistry directly revealed that 5-ABT effectively suppressed the initiation and propagation of grain boundary dissolution, significantly reducing the anodic electron transfer during polarization. Electrochemical measurements confirmed the excellent immediate and long-term inhibition performance of the 5-ABT, achieving an optimal inhibition efficiency of 95.6% (0&#xa0;h) and 97.6% (72&#xa0;h) at 6&#xa0;mM. Surface analysis verified the formation of a compact 80-nm-thick protective film, chemisorbed via Cu–N and Cu–S coordination bonds. Quantum chemical calculations identified the amino N and thiazole S/N atoms as primary active sites. It was further demonstrated that parallel adsorption via the amino nitrogen was the most stable configuration (<i>E</i>_ads =  − 1.85&#xa0;eV), complemented by vertical adsorptions through thiazole N (<i>E</i>_ads =  − 1.42&#xa0;eV) and S (<i>E</i>_ads =  − 1.11&#xa0;eV) atoms. This synergistic multi-configuration adsorption provides a superior corrosion inhibition performance of 5-ABT protective film.</p> Graphical abstract <p></p>