Background/Objectives: Graft-versus-host disease (GVHD) is a severe complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT) resulting from histocompatibility differences between donor and host cells leading to inflammation, tissue damage, and compromised patient outcome. Extracorporeal photopheresis (ECP) is considered as a second-line treatment administered to patients with GVHD who do not respond to corticosteroid treatment or who experience a relapse after an initial response and are therefore classified as steroid refractory (SR). The aim of this study is to evaluate the clinical response rates in both pediatric and adult patients with acute (a) or chronic (c) GVHD and to assess the effectiveness of ECP using the real-world data from a single center. Methods: We performed a retrospective study on 30 patients, including 11 pediatric and 19 adult patients who were treated with ECP as a second-, third-, or fourth-line therapy for (a) and (c) GVHD, alongside corticosteroids and other immunomodulatory medications. The median time from aGVHD onset to ECP was 11.5 days (range: 3 days–9 months), while for cGVHD, the median time was 90 days (range: 2 days–9 months). Results: The overall response rate (ORR) in the aGVHD patient population was 60% with a median of 9 procedures (range: 2–20). For cGVHD patients, the ORR was 70% after a median of 23.5 ECP procedures (range: 8–43). Most patients had skin involvement, with ECP achieving an ORR of 81.8% in aGVHD and 77.7% in cGVHD cases. Conclusions: ECP is a beneficial therapy for patients with (a) and (c) GVHD who have not responded to corticosteroids and other forms of immunosuppressive therapy. Specifically, ECP demonstrated efficacy in improving skin and oral symptoms and permitted reductions in or the elimination of their corticosteroid usage. The study found that extending the duration of ECP treatment was associated with better outcomes, and no detectable complications were observed over a 38-week period.