Post-COVID-19 condition (also known as long COVID) affects a substantial proportion of individuals who have been infected with SARS-CoV-2, profoundly affecting their daily lives and work. Diagnosis and prognosis of long COVID are complex and hindered by heterogeneous symptoms and the absence of validated biomarkers. This systematic review synthesises current evidence on the association between autoantibodies and long COVID, with the goal of evaluating their prognostic and diagnostic utility. Studies published in the PubMed and MEDLINE databases between Jan 1, 2020, and June 10, 2025, were considered. Study selection and quality assessment were done independently by two researchers. Of the 1113 publications screened, 44 studies met the inclusion criteria, with a total of 7571 participants, including 3372 individuals with long COVID. 31 (71%) studies reported an association between autoantibodies and long COVID; however, there was substantial heterogeneity in study design, type and timing of antibody measurements, and long COVID definitions. Several autoantibodies have been associated with long COVID occurrence, symptoms, and severity. Antinuclear antibodies, and autoantibodies targeting G protein-coupled receptors and chemokines, have emerged as potential biomarkers for aiding in the diagnosis, prognosis, and assessment of disease severity in long COVID. However, larger studies are needed to confirm the diagnostic and prognostic utility of these autoantibodies in the context of long COVID.