Previous research reported that Subclinical Narcissism (SN) may increase Mental Toughness (MT) resulting in positive outcomes such as lower psychopathy, higher school grades and lower symptoms of depression. We conducted three studies (N = 364, 240 and 144 for studies 1, 2 and 3, respectively) to test a mediation model, which suggests that SN may increase MT predicting lower Perceived Stress (PS). The participants were drawn from the general population in studies 1 and 2; and were undergraduate students in study 3. SN exerted a negative indirect effect on PS, through MT across all three studies: β = −0.26, SE = 0.039, 95% CI [−0.338, −0.187]; β = −0.25, SE = 0.050, 95% CI [−0.358, −0.160]; β = −0.31, SE = 0.078, 95% CI [−0.473, −0.168]. The results were replicated in the combined dataset. In study 3, we extended the sensitivity of the model showing that, it is the Grandiose SN that decreases PS, through MT; Vulnerable SN exhibited the reverse pattern. The findings indicate that the model, from SN to MT, may predict positive outcomes in various domains (e.g. in education and psychopathology) suggesting that inclusion of SN in the dark triad of personality may need to be reconsidered.