The dimer derivatives of ethyl acetate quinolinium bromide (Di-EAQBr) and n-butyl quinolinium bromide (DiBuQBr) were synthesized from EAQBr and BuQBr, respectively. The structure of these indolizine dimer derivatives was confirmed by high-resolution mass spectrometry and nuclear magnetic resonance techniques. These compounds were employed as new and highly effective corrosion inhibitors (CIs) for N80 steel in 15 wt% HCl. The corrosion inhibition effectiveness was evaluated using immersion and electrochemical tests. It was shown that both dimers exhibited significantly higher corrosion inhibition effectiveness compared with quinolinium salt precursors and have great potential in oilfield applications. Next, the thermodynamic and adsorption isotherm aspects thereof, as well as the corrosion inhibition mechanism, were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) and molecular dynamics (MD) simulations. The results show that both dimers exhibit higher corrosion inhibition effectiveness compared with quinolinium salt precursors, although the dosage of the dimers was only 1% of the quinolinium salts. The dimers show stronger chemisorption as assessed by Gibbs standard free energy.