Background/Objectives: Immune checkpoint inhibitors (ICIs) are increasingly used in hepatocellular carcinoma (HCC), but their application around liver transplantation (LT) remains controversial because checkpoint blockade may enhance antitumor immunity while disrupting graft tolerance. We systematically reviewed the available evidence on ICI exposure before LT and ICI therapy after LT for recurrent HCC. Methods: A PRISMA-guided systematic review with qualitative synthesis was performed. PubMed/MEDLINE, Embase, and Web of Science were searched from inception to 15 March 2026. Studies including adult patients with HCC treated with PD-1-, PD-L1-, and/or CTLA-4-targeting ICIs before LT or after LT for recurrent HCC were eligible. Results: Fifty-one studies were included. In the pre-LT setting, 25 studies reported 576 transplanted patients. Acute allograft rejection occurred in approximately 22% and graft loss in 3.8%, and shorter washout intervals were consistently associated with higher rejection risk. In the post-LT setting, 26 studies reported 117 recipients treated with ICIs; at least 22 rejection episodes (18.8%) were described, usually within 2–4 weeks of treatment initiation, with limited and inconsistent antitumor benefit. Conclusions: Pre-LT ICI use appears feasible in selected patients when adequate washout is respected. Post-LT ICI therapy remains high risk and should be reserved for highly selected cases within a multidisciplinary framework.