Pyrolysis liquid biofuel (also called bio-oil or pyrolysis oil) is a promising renewable fuel for stationary heat and power generation; however, the fuel properties, combustion performance, and combustion emissions degrade with fuel aging. The aging effects of softwood bark pyrolysis liquid biofuel on fuel properties and combustion performance are studied. To investigate the aging effects on fuel properties, the solid content, viscosity, estimated Sauter mean diameter (SMD), and thermogravimetric analysis (TGA) residue of pure pyrolysis liquid are considered. Furthermore, the CO emission, unburned hydrocarbon (UHC), and organic fraction of particulate matter (PM) emissions [also called carbonaceous residue (CR)] from combustion of the aged pyrolysis liquid biofuel/ethanol blend are measured to investigate the effect of aging on the combustion performance in a swirl spray burner. All measurements are employed for two batches of pyrolysis liquid biofuel with two levels of solid content. Results show that fuel properties, combustion emissions, and combustion performance of pyrolysis liquid become degraded as it is stored for longer periods of time. The results also support the accelerated aging correlation from the literature, which is based on viscosity and can accurately predict the effect of natural aging on the fuel properties, combustion emissions, and combustion performance.