Polydopamine-ethylene glycol dimethacrylate copolymer is a biocompatible coating with cell adhesion promotion and antibiofilm properties. This copolymer has been successfully applied on metallic implants, such as stainless steel and titanium implants, using several deposition techniques (e.g. layer-by-layer, silane activation, chemical vapor deposition, or liquid-assisted plasma polymerization). However, its application in zirconia ceramic materials, which are widely used in dentistry and medicine, has never been described. In this work, polydopamine-ethylene glycol dimethacrylate copolymer has been deposited on ultra-smooth surfaces of yttria-stabilized zirconia discs (average roughness = 2.08 ± 0.08 nm) by using liquid-assisted atmospheric-pressure plasma-induced polymerization (LA-APPiP). After the polymerization, the nanometric coating (250 nm, measured by ellipsometry) had an average roughness of 79.85 ± 13.71 nm and water contact angle of 57.8 ± 2.2 degrees, consistent with the highly hydrophilic nature of the biocompatible copolymer, if compared to the pristine zirconia (72.7 ± 2.0 degrees). The successful covalent bonding of the copolymer with the zirconia surface, thanks to the previous activation of the substrate with oxygen plasma, was proved by X-ray photoelectron spectroscopy (XPS). The polymer composition has been investigated by XPS and Raman spectroscopies. The LA-APPiP technique has been proved to be an excellent method to produce homogenous films without the need to employ solvents and further purification steps. The new copolymer film allows the uniform growth of human osteoblast-like MG-63 cells, after 7 days of cell culture, as observed by fluorescence microscopy.