<jats:sec> <jats:title>Purpose</jats:title> <jats:p>This study aims to evaluate a newly synthesized novel piperazine-based Mannich base (NPP) as a dual-function inhibitor for mitigating both electrochemical and microbiologically influenced corrosion (MIC) of L245 carbon steel in simulated shale gas flowback water.</jats:p> </jats:sec> <jats:sec> <jats:title>Design/methodology/approach</jats:title> <jats:p>NPP was synthesized via a Mannich reaction and characterized by FT-IR and 1H NMR. Its performance was assessed through 21-day weight loss measurements, electrochemical tests (OCP, EIS, potentiodynamic polarization), surface characterization (SEM, 3D profilometry and contact angle) and microbiological analyses (bacterial counts, community sequencing and water chemistry) under both sterile and non-sterile conditions.</jats:p> </jats:sec> <jats:sec> <jats:title>Findings</jats:title> <jats:p>NPP formed a hydrophobic adsorption film on the steel surface, increasing the contact angle from 65.5° to 84.4°. In the presence of corrosive microorganisms, it reduced the corrosion rate from 0.0253 mm/a to 0.0045 mm/a, achieving an inhibition efficiency of 81.9%. NPP also significantly decreased the abundance of key corrosive genera (e.g. Desulfovibrio) and suppressed sulfate-reducing activity, as evidenced by stable SO42− concentrations and negligible H2S production.</jats:p> </jats:sec> <jats:sec> <jats:title>Originality/value</jats:title> <jats:p>This work provides a potential chemical additive for corrosion control in shale gas gathering systems, demonstrating that a single molecule can address both electrochemical and microbiological corrosion challenges in complex production environments.</jats:p> </jats:sec>