Background: Endodontic treatment aims to eliminate infection and preserve the function of teeth. Single-sitting and multiple-visit root canal treatments (RCTs) are widely practiced; however, their long-term outcomes in terms of clinical success and patient satisfaction remain a topic of debate. This study evaluates and compares the shaping curve, clinical outcomes, and patient-reported outcomes of single-sitting versus multiple-visit RCTs over a 12-month follow-up period. Materials and Methods: This prospective study involved 120 patients aged 20-50 years requiring RCT for non-vital mandibular molars. Patients were randomly allocated into two groups: Group A (single-sitting, n=60) and Group B (multiple-visit, n=60). Root canals were shaped using a standardized protocol with rotary NiTi files. Post-operative pain, healing of periapical lesions (assessed radiographically), and shaping efficiency (evaluated using canal taper and curvature maintenance) were analyzed. Data collection included clinical assessments at baseline, 6 months, and 12 months, and patient-reported outcomes measured via a visual analog scale (VAS). Statistical analysis was conducted using paired t-tests and chi-square tests, with significance set at p<0.05. Results: Group A showed a shorter mean treatment time (45 ± 5 minutes) compared to Group B (120 ± 10 minutes). Post-operative pain at 24 hours was significantly lower in Group A (VAS score: 3.2 ± 0.8) than in Group B (VAS score: 4.5 ± 0.7). Radiographic healing rates at 12 months were comparable (Group A: 92%, Group B: 90%; p>0.05). The shaping curve analysis indicated similar canal taper and curvature maintenance across both groups. Patient satisfaction scores were higher for Group A (mean score: 8.5 ± 1.2) compared to Group B (mean score: 7.0 ± 1.5; p<0.01). Conclusion: Single-sitting RCT provides comparable long-term clinical and radiographic outcomes to multiple-visit RCT while reducing treatment time, post-operative pain, and improving patient satisfaction. It may be preferred in suitable cases, provided proper aseptic protocols are followed. Further multicenter studies with larger sample sizes are recommended to confirm these findings.