The widespread use of non-biodegradable plastic packaging has raised environmental and health concerns, prompting the development of sustainable alternatives. This study presents a functional paper coating composed of nanocellulose (CNFs) derived from hemp agricultural waste and modified with octadecyldimethyl(3-trimethoxysilylpropyl) ammonium chloride (ODDMAC). The modified CNFs were combined with varying concentrations of precipitated calcium carbonate (PCC) to enhance coating performance. Structural modifications were confirmed by FTIR and solid-state ¹³C-NMR, indicating the presence of alkyl and siloxane groups. Among all formulations, the PCC5%-coated paper exhibited optimal performance, with a highly hydrophobic surface (water contact angle > 150°), a significantly reduced Cobb60 value (24.45 ± 0.62 g/m²), and a low water vapor permeability (WVP) of 225.20 g·mm/m²·day·kPa, consistent with its enhanced hydrophobicity. FE-SEM analysis revealed a uniform 3 μm-thick coating layer with well-dispersed PCC particles contributing to surface roughness. The coated paper also showed improved tensile strength, excellent rub resistance (200 cycles), and strong antimicrobial activity, with reductions of Staphylococcus aureus and fungi by 99.99% and 99.92%, respectively. Biocompatibility was confirmed by 100% Caco-2 cell viability, and biodegradability reached 72.63% within 60 days. These findings demonstrate the potential of PCC5%-coated paper as a high-performance, safe, and eco-friendly alternative to plastic-based food packaging.