We used a Euclidean algorithmic method of calculating mate value discrepancies to test the hypothesis that mate value discrepancies would mediate a negative association between the Dark Triad and relationship satisfaction. Participants (N = 211) rated themselves, their partner, and their ideal partner on a set of traits known to be important in mate selection. They also completed Dark Triad and relationship satisfaction measures. We found an indirect, negative association between the Dark Triad and relationship satisfaction mediated by the Partner-Potential Partner mate value discrepancy. The higher on the Dark Triad, the more alternative partners there were that were closer to the participant's ideal mate preferences than their current partner, which was associated with decreased relationship satisfaction. This study contributes to our understanding of how the Dark Triad relates to mating psychology. These findings also highlight the utility of employing a Euclidean algorithm to understand associations between individual differences and relationship outcomes.