Hydrogen-induced intergranular stress corrosion cracking (IG-SCC) of a single edge notch sample is rapidly mitigated in the Al-Mg alloy AA5456-H116 at post-threshold, constant stress intensity of 10 MPa√m through cathodic polarization. Actively growing cracks (at -0.8 VSCE) would exhibit a reduction in growth rate of up to three orders of magnitude within an average of 20 seconds following cathodic polarization. Similar levels of mitigation in 0.6 M NaCl were achieved for polarization via a potentiostat, coupling with a pure zinc anode (with an exposed area as low as 0.03 cm2 (1 Zn : 110 AA5456 area ratio)), and an inorganic zinc-rich primer (with an exposed area as low as 0.67 cm2 (67 primer : 350 AA5456 area ratio)). Reapplication of -0.8 VSCE following 5 hours of cathodic protection caused crack growth rate increase of two to three orders of magnitude within an average of 20 seconds. Anodic current response tests on inorganic Zn-rich primer demonstrated that the primer galvanic protection is less effective in more aggressive salinity and during rapid crack growth due to a depressed anodic current response that worsens with time.