As a result of the gerotranscendence process, marital satisfaction becomes especially important in old age. At the same time, researchers emphasise that the effect of seniors’ personality on their marital satisfaction depends on many mediators. The analysis of literature suggests that one such variable might be forgiveness. Thus, the aim of the present research was to investigate whether forgiveness mediates the relationship between personality traits and marital satisfaction in late adulthood. The study involved 315 participants aged 60–75. Three psychological methods were used: (a) the Marital Satisfaction Questionnaire for Older Persons; (b) the NEO-Five Factor Inventory; and (c) the Marital Offence-Specific Forgiveness Scale. The analyses that have been undertaken revealed a number of significant associations. Neuroticism was positively related to resentment-avoidance and negatively to benevolence and marital satisfaction, whereas extraversion, agreeableness and conscientiousness were negatively correlated with resentment and positively with benevolence and satisfaction. The results also showed that both dimensions of dyadic forgiveness mediated the relationships between personality traits and marital satisfaction in ageing persons. They suggest that forgiveness of a spouse, when enhanced, could work as a buffer against the negative impact of neuroticism on marital happiness, as well as allowing the transfer of positive aspects of extraverted, agreeable and conscientious tendencies into marriage. Practical implications of the study for counselling older adults are recommended.