This study aimed to compare the effects of cervical stabilization exercises with breathing exercises and cervical stabilization exercises with thoracic spine extension exercises on respiratory function in subjects with forward head posture (FHP). The study included 30 adults with FHP. They were divided into two groups—experimental (EG) and control (CG)—with 15 participants in each group. The EG was asked to perform cervical stabilization exercises with breathing exercises, and the CG was asked to perform cervical stabilization exercises with thoracic spine extension exercises. After 4 weeks of exercise, the changes in respiratory function were measured again. The results showed significant differences in the EG before and after exercise in terms of forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), peak expiratory flow (PEF), and forced vital capacity/vital capacity max (FVC/VCmax%) (p < 0.05). The CG showed only a significant increase in FVC, FEV1, and FVC/VCmax% after the experiment (p < 0.05). In the between-group comparison, there were significant differences noted in FVC, FEV1, PEF, and FVC/VCmax% in the EG compared to the CG (p < 0.05). As a result, cervical stabilization exercises with breathing exercises are recommended to promote respiratory function.