Autism diagnoses in adulthood have risen substantially over recent years. While providing potential benefits, many autistic adults struggle to navigate their new diagnosis. Our review aimed to synthesise the evidence for post-diagnostic support for autistic adults without intellectual disability diagnosed in adulthood in the UK: investigating availability, efficacy, and autistic adults' experiences. A systematic search of four biomedical and three grey literature databases was conducted to identify UK-based studies published since 2012. A total of 27,581 records were screened in duplicate, with 19 studies regarding post-diagnostic support included. A narrative synthesis was undertaken due to anticipated heterogeneity. A service mapping exercise also provided a summary of post-diagnostic service provision currently available across the UK. Findings indicate that many services across the UK provide information and signposting as their primary form of post-diagnostic support, whereas autistic adults desire low-level support services, psychoeducation, and peer support. Evidence regarding the efficacy of post-diagnostic support was unavailable. This review highlights the need for adequate support to alleviate post-diagnostic challenges and improve autistic adults' quality of life. Low-level support services, psychoeducation, and peer support appear acceptable and feasible, with a preference often indicated for autistic-led support. Future research should develop manualised post-diagnostic support programmes and assess their efficacy.