INTRODUCTION: Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer. Photon radiotherapy shows efficacy in treating HCC but carries risks of high exit dose and radiation-induced liver disease. Additionally, HCCs with portal vein tumor thrombosis (PVTT) have a poor prognosis and are associated with higher risk of death. In recent years, proton beam therapy (PBT) has emerged as a novel treatment with the ability to downstage HCC for liver transplant (LT). AREAS COVERED: This review will provide an overview of dosimetric benefits of PBT, efficacy of PBT in treating HCC, downstaging HCC-PVTT for LT, and a comparison of PBT with other non-surgical techniques. A search of PubMed until 3 September 2024 was conducted using free search and the following keywords: hepatocellular carcinoma, proton beam therapy, portal vein tumor thrombosis, local ablative therapy, trans-arterial chemoembolization, stereotactic body radiotherapy, Y-90 radioembolization. EXPERT OPINION: Various clinical trials using PBT have shown promising tumor local control and overall survival rates. PBT is mostly safe and efficacious for downstaging HCC-PVTT for LT. PBT has also been shown to be non-inferior to various other treatment modalities. Future research should focus on combinations of PBT with other modalities.