The article investigates the chemical and rheological properties of bituminous binders extended with tall oil pitch (TOP), a bio-oil by-product from the pulp and paper industry. Bio-extended binders were formulated to incorporate different percentages of TOP, reaching the target penetration grades. Comprehensive chemical analyses, including Fourier-transform infrared FTIR spectroscopy and SARA (saturates, aromatics, resins, and asphaltenes) analysis by thin-layer chromatography with flame ionisation detection (TLC-FID), were conducted to investigate the compositional changes induced by TOP addition. Laboratory ageing of the binders was carried out. Rheological characterisation was performed using dynamic shear rheometer (DSR) to assess the impact on viscoelastic behaviour. The results indicate that TOP-extended bituminous binders exhibit distinct chemical signatures from bitumen, with notable differences in functional groups and SARA fractions. Furthermore, the incorporation of TOP changes the viscoelastic behaviour of binder. The specific impact and its extent seem to depend on the temperature and frequency range as well as the content of TOP in the binder. These findings are expected to contribute to the development of more sustainable asphalt pavements, highlighting the potential of TOP as a viable extender for bituminous binders.