Belief in a Just World (BJW) can be categorised into domains of how people view the fairness of their immediate social worlds (Personal Belief in a Just World–PBJW) and the wider world (General Belief in a Just World–GBJW). We conducted two studies with 179 (Study 1) and 364 (Study 2) participants to examine differential relationships that PBJW and GBJW could have in directly predicting mental wellbeing and depression and indirectly via three mediators of perceived control, optimism, and gratitude. Path analyses examined how well data from each study fit 13 different models. Models 1 to 4 tested whether PBJW directly and indirectly via the three mediators predicted wellbeing (Model 1) and depression (Model 3) and if GBJW likewise directly and indirectly predicted wellbeing (Model 2) and depression (Model 4). These four models had the best supported statistical fit for either Study 1 or 2 relative to other models. In both studies when explaining the effect of PBJW on wellbeing and depression, perceived control was the strongest mediator, followed by optimism, and then gratitude. When examining the effect of GBJW on wellbeing and depression, only perceived control and optimism were significant mediators. These studies affirm the need to assess GBJW and PBJW as separate phenomena, rather than combining these constructs or omitting PBJW, as is sometimes done.