This study assessed the extent to which being predisposed towards engaging in acts of gratitude and forgiveness is associated with enhanced quality of life (QoL), and whether these associations are mediated by positive and negative affective states. The study sample comprised 327 people with one of three chronic illnesses (arthritis, chronic obstructive pulmonary disease and diabetes). Participants completed self-report measures of two positive predispositions (the tendencies towards gratitude and forgiveness), two affective states (positive and negative) and three indices of QoL (physical, psychological and satisfaction with life). As hypothesised, gratitude, and to a lesser extent forgiveness, predicted enhanced QoL, with most effects mediated via increased positive affect. Findings support the view that predispositions towards interpersonal gratitude, and possibly interpersonal forgiveness, may bolster the QoL of people living with chronic physical illness. Consistent with contemporary theories of positive emotion, gratitude appears to have its effects via enhancing positive affect. The study adds to the emerging evidence that a predisposition towards gratitude benefits QoL and extends past findings by identifying a mechanism that is important in people with chronic illnesses.