The purpose of this study was to examine the predictive capability of a habit construct, controlling for intention and perceived behavioral control, with moderate and strenuous intensity physical activity. This approach was expanded through an examination of whether conscious deliberation in the initiation of physical activity would attenuate these findings and a test of the intention-habit interaction. Participants were 337 undergraduate students who completed the habit measure and measures of intention, deliberation, and perceived behavioral control phrased in either moderate or vigorous intensities at time 1. This was followed by a measure of behaviour 2 weeks later. Results using stacked structural equation models (moderate and vigorous intensity) demonstrated the direct effect of habit and accounted for a significant effect on physical activity after controlling for intention and perceived behavioral control; this effect was invariant to intensity and conscious deliberation. A 3-way interaction, however, was identified for the habit X intention relationship and intensity. In the moderate intensity condition, individuals who reported higher habits showed a lower intention-behavior relationship when compared with those who reported modest or low habits. By contrast, individuals who reported high habit levels in the vigorous physical activity condition demonstrated a larger intention-behavior relationship than their modest and low habit counterparts. The results support the notions that some properties of physical activity may have an automatic component and that habits may be important to physical activity action initiation.