A novel ultrasound-based approach for the deposition of an octacalcium phosphate (OCP) and nanocrystalline apatite (ncAp)-based coating on the magnesium alloy AZ31 as a biodegradable implant material is established. The studies consider both the structural analysis and the resulting corrosion protection and correlate the related findings with cytocompatibility. The ultrasound-based approach is shown to lead to the deposition of an OCP and ncAp-based coating with a trilayer structure on AZ31. The coatings consist of two inner compact layers and an open porous top layer. The formation of the functional OCP/ncAp coating and deposition on the AZ31 surface take place within minutes in a single processing step and do not require any pre-heating, mediators or post-deposition treatment for the achievement of corrosion protection and cytocompatibility. The obtained coatings were characterized by means of FTIR and Raman spectroscopy as well as FE-SEM and X-ray crystallography. Electrochemical impedance spectroscopy revealed corrosion inhibition especially in the initial phase after immersion in physiological electrolyte. Moreover, this corrosion protection resulted in a strongly improved cytocompatibility of AZ31 as verified by in vitro viability tests using human mesenchymal stromal cells.