Previous studies investigated the connection between personality and relationship outcomes. Expanding previous work, the current study examined the concurrent relationship between dark personality and marital instability and further explored its mechanism in an actor-partner interdependence mediation model. The present study recruited 260 married Chinese couples and collected self- and partner-ratings of Machiavellianism and psychopathy using the Mach-IV and the Levenson self-report psychopathy scale. In addition, we measured marital quality and marital instability using the quality marriage index and the marital instability scale (short form), respectively. Results showed that both Machiavellianism and psychopathy had indirect actor-partner effects on marital instability. Furthermore, self- and partner-rating Machiavellianism and psychopathy are more likely to affect marital instability by full mediation of marital quality. In conclusion, marital quality plays a complete mediating role between dark personality and marital instability. The current study enriches the theoretical framework of the relationship between personality and relationship consequence and provides great practical significance for maintaining a close relationship.