This research aimed to develop a brief, multi-factorial Factors Related to Forgiveness Inventory (FRFI), assessing social-cognitive factors that facilitate or inhibit forgiveness. In total, 512 participants completed a questionnaire, reporting trait forgivingness, and describing a specific transgression, characteristics of the offence or offender, beliefs about forgiving the offender, overall forgiveness and revenge, avoidance, and benevolence motivations toward the offender. Exploratory and confirmatory factor analyses suggested seven factors including positive post-transgression offender responses, perceived likelihood of the offender repeating offences, valuing the relationship with the offender, social influences to not forgive, believing forgiveness would be condoning or excusing the offence, intent of the offender, and spiritual beliefs about forgiveness. Construct, criterion, and incremental validity were assessed and supported validity of scores of the seven FRFI subscales for 415 adults. All subscales explained unique variance in overall forgiveness. Furthermore, FRFI subscales accounted for between 21% and 59% of variance in forgiveness-related constructs, after trait forgivingness was accounted for. One-week test-retest reliability suggested scores were temporally stable. The FRFI has potential for use in future research into factors facilitating and inhibiting forgiveness and in therapeutic contexts.