Background: Chronic low back pain (CLBP) associated with sedentary occupations is influenced by prolonged sitting, poor posture and physical deconditioning. Objective: To evaluate the effectiveness of individualized ergonomic intervention combined with progressive exercise therapy compared with conventional physiotherapy on pain intensity and functional disability. Methods: A two-arm, parallel-group, assessor-blinded randomized controlled trial was conducted in 60 sedentary employees aged 25–50 years with CLBP of more than 3 months. Participants were randomized equally to Group A, receiving individualized workstation correction combined with progressive strengthening and flexibility exercises, or Group B, receiving conventional physiotherapy, for 3 sessions/week for 8 weeks. VAS and ODI were assessed before and after intervention. Results: Group A VAS decreased from 7.13 ± 0.82 to 1.93 ± 0.78 and ODI from 40.40 ± 4.11 to 13.03 ± 2.63. Group B VAS decreased from 7.00 ± 0.74 to 3.83 ± 0.87 and ODI from 39.60 ± 3.73 to 23.60 ± 4.00. Between-group comparisons favoured Group A for both VAS and ODI (p < 0.001). Conclusion: Individualized ergonomic intervention combined with progressive exercise therapy was more effective than conventional physiotherapy exercise alone in reducing pain and functional disability in chronic sedentary occupational low back pain.