Introduction This study investigated whether the Big Five personality dimensions were associated with mental health trajectories and/or intervention effects of a digital divorce intervention from juridical divorce to 12 months following juridical divorce. The study utilized a randomized controlled trial study design (N = 676) and measured mental health outcomes (anxiety, depression, somatization, and stress) at study inclusion (i.e., at juridical divorce) and 3-, 6-, and 12 months after juridical divorce. Big Five personality dimensions were measured 1 month post study inclusion. Results The study found that neuroticism is the personality dimension most predictive of post-divorce mental health outcomes. Specifically, divorcees with higher neuroticism scores indicated worse mental health immediately following divorce, but their symptom levels decreased more rapidly over a 12 months period after juridical divorce compared with lower neuroticism divorcees. It is also notable that their mean scores for the mental health outcomes remained higher at all time points (3, 6, and 12 months post baseline), relative to those lower in neuroticism. Conclusion Findings are discussed in light of divorce-adjustment-theory and the stress-buffering model.