Previous research has indicated that autistic individuals report lower quality of life (QoL) than non-autistic people. It is unclear whether it is the autism traits themselves or co-occurring thinking styles or mental health difficulties that most impair QoL. This study tested a hypothesised model to explore how 'intolerance of uncertainty' (IU), alexithymia (difficulty in identifying and describing own emotions), and anxiety play into the association between autistic traits and QoL. Online survey data were analysed from 116 autistic and 51 non-autistic adults who completed six standardised questionnaires measuring autistic traits, alexithymia, IU, anxiety and QoL (physical health, psychological health, social relations, and environment domains). The autistic group reported higher scores for alexithymia, IU and anxiety, and lower scores for QoL across domains, compared to the non-autistic group. Across the entire sample, autistic traits, alexithymia, IU and anxiety were positively correlated with one another, and negatively related to the four domains of QoL. Finally, IU and anxiety partially serially mediated the pathways from autistic traits to physical health and environment domains of QoL, and fully mediated the pathways from autistic traits to psychological health and social relations domains of QoL, across the full sample. The lower QoL experienced by autistic people may be explained in part by the mediating effect of both IU and anxiety (but not alexithymia). This study highlights the need for evidence-based interventions to address both IU and anxiety to improve QoL for autistic people/those with high levels of autistic traits.