Neuroticism is a relatively stable personality trait characterized by negative emotionality (for example, worry and guilt) ; heritability estimated from twin studies ranges from 30 to 50% , and SNP-based heritability ranges from 6 to 15% . Increased neuroticism is associated with poorer mental and physical health , translating to high economic burden . Genome-wide association studies (GWAS) of neuroticism have identified up to 11 associated genetic loci . Here we report 116 significant independent loci from a GWAS of neuroticism in 329,821 UK Biobank participants; 15 of these loci replicated at P < 0.00045 in an unrelated cohort (N = 122,867). Genetic signals were enriched in neuronal genesis and differentiation pathways, and substantial genetic correlations were found between neuroticism and depressive symptoms (r  = 0.82, standard error (s.e.) = 0.03), major depressive disorder (MDD; r  = 0.69, s.e. = 0.07) and subjective well-being (r  = -0.68, s.e. = 0.03) alongside other mental health traits. These discoveries significantly advance understanding of neuroticism and its association with MDD.