This study aimed at estimating the extent to which a combination therapy of low-level laser therapy (LLLT) with exercise and orthotic support (usual care) affects functional ability in the patient with plantar fasciitis (PF) when compared to usual care alone. Participants with PF were randomly allocated into two groups: LLLT (n = 27) and control (n = 22). All the participants received home exercise program with orthotic support. In addition, the LLLT group received a gallium-aluminum-arsenide laser with a 850-nm wavelength for ten sessions, three times a week. Functional outcomes were measured by function subscale of American Orthopedic Foot and Ankle Society Score (AOFAS-F) and 12-min walking test including walking speed, cadence, and activity-related pain using visual analog scale (VAS).The scores were recorded at baseline, third week, and third month after the treatment. Analysis was performed using repeated measures ANOVA and an intention to treat approach using multiple imputations. There was a significant improvement in AOFAS-F total score at 3 weeks in both groups (LLLT, p < 0.001; control, p = 0.002), but the improvements were seen only for the LLLT group for AOFAS-F total score (p = 0.04) and two individual items of AOFAS-F (walking distance (p < 0.001) and walking surface (p = 0.01)) at 3 months. The groups were comparable with each other for both walking speed and cadence at all assessment times (p > 0.05). Both groups showed significant reduction in pain over 3 months (LLLT, p < 0.001; control, p = 0.01); however, the LLLT group had lower pain than the control group at 3 months (p = 0.03). The combination therapy of LLLT with usual care is more effective to improve functional outcomes and activity-related pain when compared to usual care alone.