Background Intention is theorized as the proximal determinant of behavior in many leading theories and yet intention–behavior discordance is prevalent. Purpose To theme and appraise the variables that have been evaluated as potential moderators of the intention–physical activity (I-PA) relationship using the capability–opportunity–motivation– behavior model as an organizational frame. Methods Literature searches were concluded in August 2020 using seven common databases. Eligible studies were selected from English language peer-reviewed journals and had to report an empirical test of moderation of I-PA with a third variable. Findings were grouped by the moderator variable for the main analysis, and population sample, study design, type of PA, and study quality were explored in subanalyses. Results The search yielded 1,197 hits, which was reduced to 129 independent studies (138 independent samples) of primarily moderate quality after screening for eligibility criteria. Moderators of the I-PA relationship were present among select variables within sociodemographic (employment status) and personality (conscientiousness) categories. Physical capability, and social and environmental opportunity did not show evidence of interacting with I-PA relations, while psychological capability had inconclusive findings. By contrast, key factors underlying reflective (intention stability, intention commitment, low goal conflict, affective attitude, anticipated regret, perceived behavioral control/self-efficacy) and automatic (identity) motivation were moderators of I-PA relations. Findings were generally invariant to study characteristics. Conclusions Traditional intention theories may need to better account for key I-PA moderators. Action control theories that include these moderators may identify individuals at risk for not realizing their PA intentions. Prospero # CRD42020142629.