Excessive time spent in sedentary behavior (SB) is associated with numerous health risks. These associations remain even after controlling for physical activity (PA) and body mass index, indicating that efforts to promote leisure time PA alone are insufficient. Social-cognitive and motivation variables represent potentially modifiable factors and have the potential of furthering our understanding of sedentary behavior. Hence, a review was conducted to summarize the relation between social-cognitive and motivational factors and SB. Four databases were searched and a total of 4866 titles and abstracts were reviewed. Twenty-five studies met the inclusion criteria, assessing 23 different social-cognitive and motivational factors. Seventeen studies were theory-based and 8 did not employ a theoretical model. Results showed that among SB-related cognitions, risk factors for greater sedentary time included having more positive attitudes towards SB, perceiving greater social support/norms for SB, reporting greater SB habits, having greater intentions to be sedentary, and having higher intrinsic, introjected, and external motivation towards SB. Protective factors associated with lower sedentary time included having greater feelings of self-efficacy/control over SB and greater intentions to reduce SB. Among PA-related cognitions, protective factors included more positive attitudes towards PA, greater social support/norms for PA, greater self-efficacy/control for PA, higher PA intentions, and higher intrinsic and identified motivation towards PA. In conclusion, a number of social-cognitive and motivational factors were identified that were associated with sedentarism. To further extend our understanding of the relation between these factors and SB, more longitudinal, theory-driven studies examining cognitions and motivation from a sedentary perspective are required.