Given the important associations between couple conflict and various physical and mental health outcomes, it is essential to explore factors that may catalyze or exacerbate the frequency and impact of conflict in romantic relationships. One such factor may be relationship mindfulness, or the tendency to have a nonjudgmental awareness of one’s experiences in romantic relationships. Previous research has demonstrated a link between relationship mindfulness and various relational outcomes, but its association with relationship conflict has not yet been explored. Additionally, the current study sought to explore the mechanisms that link relationship mindfulness and relational outcomes. Based on previous research connecting conflict to negative partner attributions, the study examined how relationship mindfulness may predict conflict through negative partner attributions. Furthermore, the study aimed to incorporate loneliness as a potential mediator between relationship mindfulness and negative partner attributions. A sample of 116 different-sex middle-aged married couples were recruited to complete an online assessment. Using an actor–partner interdependence mediation model, the results indicated several significant associations among relationship mindfulness, negative partner attributions, loneliness, and relationship conflict. For example, a significant indirect effect was found; that is, female relationship mindfulness was associated with decreased relationship conflict via its prior association with both male loneliness and additionally through male loneliness and subsequent male negative partner attributions. The results indicate that by employing interventions that increase relationship mindfulness, it may be possible to both reduce loneliness and encourage more charitable partner attributions which, in turn, may reduce couple conflict.