Graphene-coated textiles are attracting increasing interest due to their electrical conductivity, flexibility, and durability, making them promising materials for wearable electronics, energy storage, and smart fabrics. However, the influence of graphene loading on the overall performance of textile substrates remains insufficiently explored. In this study, flax textiles were coated with controlled amounts of graphene using a sustainable process and systematically characterized. Raman spectroscopy and FE-SEM analyses confirmed uniform graphene deposition, while TGA enabled quantification of the graphene loading. FTIR results indicated that the chemical structure of the flax fibers remained preserved after coating. The graphene layer modified the surface properties, transforming the textile from hydrophilic to hydrophobic and slowing its natural biodegradation. Electrical conductivity increased with graphene content, with a sharp transition occurring above 2 wt%, where the fabric became conductive. At approximately 3 wt% graphene, the textile exhibited excellent electrothermal heating performance, reaching 180 °C under an applied voltage of 20 V. Photothermal experiments showed that the temperature increased to about 70 °C after 5 minutes of solar exposure. This temperature rise was sufficient to induce a bactericidal effect under sunlight, effectively inhibiting bacterial growth. These results demonstrate that controlled graphene deposition can effectively tailor the multifunctional properties of flax textiles, combining flexibility, environmental sustainability, and efficient thermal management. Such materials show strong potential for applications in solar-heated garments, self-disinfecting fabrics, and solar-driven water purification.