The associations between couple members' personality and their relationship satisfaction can be conceptualized as reciprocal transactions. To better understand these transactions, we focused on both partners' interpersonal vulnerabilities (i.e. neuroticism, low self‐esteem, and insecure attachment); daily emotional, cognitive, and behavioural relationship components (i.e. perceived responsiveness, positive expectations, and self‐disclosure); and relationship satisfaction. Specifically, we examined whether the average levels and within‐person variability of the relationship components mediated the transactions between interpersonal vulnerabilities and relationship satisfaction. Data came from 689 female–male couples aged 18 to 81 years who participated in three measurement occasions across 12 months, including a 14‐day diary phase. We used mediated dyadic bivariate latent change score models to test the level–change and change–change transactions and mediations. The findings partly supported our hypotheses: Couple members with interpersonal vulnerabilities had lower average levels (but not higher within‐person variability) of the relationship components, and less satisfied couple members had lower average levels and higher within‐person variability of these components. The lower average levels but not the variability mediated between a lower level of relationship satisfaction and an increase in avoidant attachment. No other mediations were observed. We discuss the importance of studying daily relationship components for better understanding reciprocal transactions in couples. © 2020 European Association of Personality Psychology