Background: People with spinal cord injury (SCI) are more susceptible to sedentary lifestyles because of the displacement of physical functioning and the copious barriers. Benefits of physical activity for people with SCI include physical fitness, functional capacity, social integration and psychological well-being. Objective: The purpose of this study was to develop and test a social cognitive theory-based instrument aimed to predict physical activity among people with SCI. Methods: An instrument was developed through the utilization and modification of previous items from the literature, an expert panel review, and cognitive interviewing, and tested among a sample of the SCI population using a cross-sectional design. Statistical analysis included descriptives, correlations, multiple regression, and exploratory factor analysis. Results: The physical activity outcome variable was significantly and positively correlated with self-regulatory efficacy (r = 0.575), task self-efficacy (r = 0.491), self-regulation (r = 0.432), social support (r = 0.284), and outcome expectations (r = 0.247). Internal consistency for the constructs ranged from 0.82 to 0.96. Construct reliability values for the self-regulation (0.95), self-regulatory efficacy (0.96), task self-efficacy (0.94), social support (0.84), and outcome expectations (0.92) each exceeded the 0.70 a priori criteria. Conclusions: The factor analysis was conducted to seek modifications of current instrument to improve validity and reliability. The data provided support for the convergent validity of the five-factor SCT model. This study provides direction for further development of a valid and reliable instrument for predicting physical activity among people with SCI.