This study followed a pre-registered analysis plan with the aim to investigate whether autistic traits and self-compassion are correlated in autistic adults, and to test an indirect effect of autistic traits on anxiety/depression via self-compassion. We present the findings of an online survey of 456 participants (n = 228 autistic adults, n = 228 non-autistic adults) who completed the Autism Spectrum Quotient (AQ), the Self-Compassion Scale (SCS) and the Hospital Anxiety and Depression Scale (HADS). Lower self-compassion was reported by autistic participants compared to non-autistic participants, and a negative correlation was found between autistic traits and self-compassion in both groups. Furthermore, an indirect association between autistic traits and anxiety/depression via self-compassion was observed in both samples. Considering that many autistic people experience co-occurring anxiety and depression, and that self-compassion is a skill that can be cultivated with practice, the findings of this study suggest that self-compassion may be a modifiable factor that could improve the mental health of this population.