Interface-active, metal-organic complexes (MOCs) have been extensively exploited for interface engineering due to their material-independent coating properties. However, the MOC-based films often face some challenges, such as dark coloration and synthetic difficulty in organic-ligand derivatives, limiting their functional potential and expandability. This paper reports the fabrication of transparent MOC films, composed of Zr⁴⁺ ions and trimesic acid (BTC), under mild aqueous conditions and their facile chemical functionalization. In situ supramolecular self-assembly of Zr-BTC MOCs resulted in robust films on diverse substrates, regardless of their physicochemical properties, which exhibited remarkable stability under acidic conditions and in organic solvents. Notably, the simple chemical structure of BTC enabled a straightforward preparation of functional derivatives, exemplified by the incorporation of polymerization initiator-conjugated BTC ligands into Zr-BTC MOC films. Subsequent surface-initiated polymerization led to the formation of zwitterionic polymer brushes, imparting antifouling properties. Overall, this work provides the potential usage of Zr-BTC MOCs as a versatile molecular toolbox for interface engineering.