The biodegradation behavior of Mg, coated by polymethyl methacrylate as well as polymethyl methacrylate (PMMA)-bioactive glass (BG) composite was investigated. Electrophoretic deposition and dip coating techniques were adopted to prepare composite coating using a suspension of different percentages of the above two chemical materials. The deposited coatings were characterized using SEM, EDS, FTIR, and water contact angle measurements. Biodegradation behavior study of the coated Mg was performed using linear polarization, impedance spectroscopy, and immersion tests in simulated body fluid. The compact and homogeneous composite coating was developed as evidenced by electron microscopy results. The water contact angle measurement showed a 44° increase in the contact angle of the composite coated Mg compared to the uncoated one. The composite coating was covered by a bone-like hydroxyapatite layer after 336 h, indicating that the coating has an excellent in vitro bioactivity. The electrochemical testing results confirmed a significant reduction, 96.9%, in the biodegradation rate of Mg coated with the composite prepared from 45 g/L PMMA + 3.5 g/L 45S5 GB suspension compared to that of the uncoated one. Therefore, the composite coated Mg can be proposed as a promising material for biodegradable implant application.