<p>Sleep quality is a fundamental determinant of psychological well-being, yet individuals with Autism Spectrum Disorder (ASD) frequently experience substantial sleep disturbances that may intensify existing mental health vulnerabilities. This systematic review synthesizes peer-reviewed research published between 2015 and 2025 to examine the association between sleep quality and psychological outcomes among individuals with ASD. A comprehensive search across PubMed, PsycINFO, Scopus, and Web of Science yielded 25 eligible studies employing cross-sectional, longitudinal, and quasi-experimental and randomized controlled trial designs, with participants ranging in age from approximately 3 years to over 80 years. Methodological quality and risk of bias of the included studies were systematically appraised using a structured critical appraisal framework, and findings were synthesized narratively due to methodological heterogeneity. Findings across diverse cultural and clinical contexts consistently demonstrate that poor sleep quality is associated with heightened symptoms of anxiety and depression, reduced executive functioning, and greater difficulties in emotional and behavioral regulation. Several studies also identified moderating and mediating factors—such as ASD symptom severity, developmental stage, and co-occurring conditions—that shape the strength and direction of these associations. Collectively, the evidence positions sleep health as a modifiable and high-impact intervention target capable of improving psychological outcomes and overall quality of life for individuals with ASD. Integrating comprehensive sleep assessment and evidence-based sleep interventions into multidisciplinary care frameworks is strongly recommended. This systematic review was conducted without meta-analysis, and future research should prioritize longitudinal, multi-method designs to clarify causal mechanisms and address critical gaps related to underrepresented groups, including autistic females and older adults.</p>