Gliomas are the most common primary malignant brain tumors, with a poor prognosis and high mortality, and there is no effective treatment regimen. A number of studies have shown that replication protein A3 (RPA3) can regulate DNA replication and that the abnormal expression of RPA3 can lead to genomic instability and induce the development of a variety of tumors. However, the relationship between RPA3 and gliomas and the mechanism of action remains unclear. In this study, we investigated the role of RPA3 in the development of gliomas and the possible mechanism. The Chinese Glioma Genome Atlas (CGGA), The Cancer Genome Atlas (TCGA), and the Gene Expression Omnibus (GEO) databases were used to analyze the expression level of RPA3 and its correlation with clinical prognosis. A univariate Cox regression model was established to predict the prognosis of glioma patients and analyze the correlation between RPA3 and immune cell infiltration and activation. Immunohistochemistry, RT-PCR, and Western blot (WB) were used to detect the expression of RPA3 in glioma specimens. After knocking down and overexpressing RPA3 with plasmids, effects on glioma cell proliferation, migration and invasive capacity were investigated in vitro. The possible molecular mechanisms were analyzed using WB. Results showed that the expression of RPA3 in glioma tissue and cells was significantly higher than that in normal glial cells and was positively correlated with the poor prognosis of patients with gliomas. The overexpression of RPA3 expression activated the phosphatidylinositol 3-kinase (PI3K)-AKT-mammalian target of the rapamycin (mTOR) pathway by promoting the phosphorylation of PI3K, AKT, and mTOR, thereby promoting the proliferation, migration and invasion of glioma cells. In conclusion, RPA3 is highly expressed in gliomas and promotes the proliferation, migration and invasion of gliomas by activating the PI3K-AKT-mTOR pathway. Therefore, RPA3 may be a prognostic biomarker and therapeutic target for gliomas.