Cellulose nanofibers (CNFs) are the most advanced bio-nanomaterial utilized in various applications due to their unique physical and structural properties, renewability, biodegradability, and biocompatibility. It has been isolated from diverse sources including plants as well as textile wastes using different isolation techniques, such as acid hydrolysis, high-intensity ultrasonication, and steam explosion process. Here, we planned to extract and isolate CNFs from carpet wastes using a supercritical carbon dioxide (Sc.CO2) treatment approach. The mechanism of defibrillation and defragmentation caused by Sc.CO2 treatment was also explained. The morphological analysis of bleached fibers showed that Sc.CO2 treatment induced several longitudinal fractions along with each fiber due to the supercritical condition of temperature and pressure. Such conditions removed th fiber’s impurities and produced more fragile fibers compared to untreated samples. The particle size analysis and Transmission Electron Microscopes (TEM) confirm the effect of Sc.CO2 treatment. The average fiber length and diameter of Sc.CO2 treated CNFs were 53.72 and 7.14 nm, respectively. In comparison, untreated samples had longer fiber length and diameter (302.87 and 97.93 nm). The Sc.CO2-treated CNFs also had significantly higher thermal stability by more than 27% and zeta potential value of −38.9± 5.1 mV, compared to untreated CNFs (−33.1 ± 3.0 mV). The vibrational band frequency and chemical composition analysis data confirm the presence of cellulose function groups without any contamination with lignin and hemicellulose. The Sc.CO2 treatment method is a green approach for enhancing the isolation yield of CNFs from carpet wastes and produce better quality nanocellulose for advanced applications.