Background: Physical activity (PA) counseling is becoming commonplace in primary care settings, although there is a high degree of variation in the quality and quantity of this intervention. The purpose of this review was to examine the theory on which the intervention is based and the level of treatment fidelity applied at all stages of the intervention.Methods: A systematic review was carried out for interventions that reported an element of PA counseling. Results were mapped according to a treatment fidelity framework of intervention design, training, delivery, receipt, and enactment.Results: Most studies were underpinned by the transtheoretical model. Few studies described the frequency or duration of PA counseling training or competence level of the interventionist. The most common outcome measures were behavioral and physiological, with few studies including a cognitive outcome measure.Conclusions: Most research focuses on outcome and significance rather than intervention processes, with limited consideration of treatment fidelity. The design, training, delivery, and receipt of PA counseling should be reported more thoroughly.