Trait mindfulness has been linked to romantic relationship satisfaction, but what are the mechanisms of action that give rise to this association? The current study tested the possible mechanism of perceived responsiveness in a partner (i.e., perceiving that a romantic partner is understanding, validating, and caring) who had the opportunity to provide support. We hypothesized that individuals higher in trait mindfulness would rate their partners higher in responsiveness, which in turn would predict greater relationship satisfaction in the rater. We also examined a cross-dyad path, in which partners of more mindful participants would view them as more responsive and thus have greater relationship satisfaction. In a laboratory study, each member of 127 heterosexual couples (n = 254) completed measures of trait mindfulness and relationship satisfaction. Couple members later took turns discussing a personal concern and then reported their partner’s responsiveness during that conversation. An actor-partner interdependence mediation model revealed that perceived responsiveness mediated the mindfulness and relationship satisfaction association. Participants higher in Non-judgment and Observing facets of trait mindfulness rated their partners higher in responsiveness, which predicted relationship satisfaction. In addition, participants higher in Acting with Awareness both (1) rated their partners as higher in responsiveness, and (2) were perceived by their partners as more responsive, with both paths mediating effects on relationship satisfaction. The results for Acting with Awareness, however, should be interpreted with caution, due to poor model fit. Thus, mindfulness may facilitate relationship satisfaction through heightened perception of partners’ responsiveness both within and across dyads.