Background In this study, the effect of adding a smartphone app to an 8-week global postural reeducation (GPR) on neck pain, endurance, quality of life, and forward head posture (FHP) in patients with chronic neck pain and FHP was evaluated. Methods Sixty male and female office workers (38.5 ± 9.1 years) with chronic neck pain were randomly assigned into three groups: group 1 (GPR+ a smartphone app, n = 20), group 2 (GPR alone, n = 20), and group 3 (the control group, n = 20). The primary outcome was pain and the secondary outcomes were disability, quality of life, endurance, and posture. Pain, disability, endurance, quality of life, and posture were evaluated using the visual analog scale (VAS), neck disability index (NDI), progressive iso-inertial lifting evaluation (PILE) test, quality of life questionnaire (SF-36), and photogrammetry, respectively, at pre-and post-8-week interventions. A one-way analysis of covariance (ANCOVA) has been conducted to statistically analyze the data. Results The GPR+ a smartphone app had statistically significant improvements versus GPR alone in pain (mean difference, − 2.05 ± 0.65, ES (95% CI) − 0.50 (− 1.04 to − 0.01), P = 0.04), disability (difference = 11.5 ± 1.2, ES (95% CI) = 0.31 (0.22 to 0.97), p = 0.033), FHP (difference = 1.6 ± 0.2, ES (95% CI) = 0.31 (0.09 to 0.92), p = 0.047), and endurance (difference = 2 ± 3.3, ES (95% CI) = 0.51 (0.02 to 1.03), p = 0.039). Both of the GPR+ a smartphone app and GPR alone groups had statistically significant differences versus the control group in all outcomes. Conclusion When a workplace assessment and management could not be as part of any intervention, adding a smartphone app to GPR for NP may be an appropriate tool to administer a home and work exercise program resulting in elevating pain and disability, as well as improving FHP and endurance. Trial registration Current Controlled Trials using the UMIN-RCT website UMIN000039720. Retrospectively registered on January 9, 2020.