Motivated by collective emotions theories that propose emotions shared between individuals predict group level qualities, we hypothesized that co-experienced affect during interactions is associated with relationship quality, above and beyond the effects of individually-experienced affect. Consistent with Positivity Resonance Theory, we also hypothesized that co-experienced positive affect would have a stronger association with relationship quality than co-experienced negative affect. We tested these hypotheses in 150 married couples across three conversational interactions: a conflict, neutral, and pleasant topic. Spouses continuously rated their individual affective experience during each conversation while watching video-recordings of their interactions. These individual affect ratings were used to determine, for positive and negative affect separately, the number of seconds of co-experienced affect and individually-experienced affect during each conversation. In line with hypotheses, results from all three conversational topics suggest that more co-experienced positive affect is associated with greater marital quality, whereas more co-experienced negative affect is associated with worse marital quality. Individual level affect factors added little explanatory value beyond coexperienced affect. Comparing co-experienced positive affect and co-experienced negative affect, co-experienced positive affect generally outperformed co-experienced negative affect, although co-experienced negative affect was especially diagnostic during the pleasant conversational topic. Findings suggest co-experienced positive affect may be an integral component of high-quality relationships and highlight the power of coexperienced affect for individual perceptions of relationship quality.