Recent empirical findings suggest that greater belief in free will predicts positive behavioral outcomes, such as lowered aggression, decreased cheating, bettered work performance, and improved learning. To expand on this research, the current investigation re-examines the link between stronger belief in free will and pro-social behavior in the context of transgressions in interpersonal relationships. Taking into account that one’s philosophical beliefs can fluctuate in strength and across time, we conducted a daily diary survey of 85 undergraduates who reported interpersonal offenses for 14 days. Data were analyzed with a multi-level approach. We found that believing more strongly in free will was associated with greater decisional forgiveness, but was unrelated to emotional forgiveness. Higher levels of belief in scientific determinism, on the other hand, were related to greater emotional forgiveness. These relationships were not mediated by relationship attributions.