Parents face numerous barriers to exercise and exhibit high levels of inactivity. Examining theory-based determinants of exercise among parents may inform interventions for this population. The purpose of this study was to test a social-cognitive model of parental exercise participation over a 12-month period. Mothers (n = 226) and fathers (n = 70) of children <16 completed measures of exercise, barriers self-efficacy, perceived barriers, and exercise planning at baseline and 1 year later. Panel analyses were used to test the hypothesized relationships. Barriers self-efficacy was related to exercise directly and indirectly through perceived barriers and prioritization/planning. Prioritization and planning also mediated the relationship between perceived barriers and exercise. These paths remained significant at 12 months. These results suggest efforts to increase exercise in parents should focus on improving confidence to overcome exercise barriers, reducing perceptions of barriers, and helping parents make specific plans for prioritizing and engaging in exercise.