The application of a biodegradable conducting polymer coating based on a polythiophene composite (PTC) to mitigate degradation of magnesium in an in vitro environment is reported. The rationale behind the study is to advance a bioactive coating to control the rapid early stage degradation of the magnesium and prevent inflammatory reactions and physiological complications, while, in the long term, the coating degrades, followed by the full degradation of the magnesium implant. The conducting polymer in this study is deposited on a bioabsorbable medical grade magnesium alloy, AZNd, through layer-by-layer deposition, and the degradation behavior in simulated biological fluid is studied electrochemically. The possibility of a synergistic effect by combining praseodymium conversion coating together with the conducting polymer coating in protecting magnesium is also examined. Results show that the highest level of corrosion mitigation is afforded by the combination of praseodymium conversion and the conducting polymer coating layers. Electrochemical models are advanced to explain the electroactivity of the conducting polymer across the film as well as at the interface with electrolyte and substrate. Based on the physical and electrochemical evidence, the barrier effect is proposed as the main protection mechanism.