Human leukocyte antigen G (HLA‐G), a nonclassic HLA class Ib molecule involved in the maintenance of maternal tolerance to semiallogeneic fetal tissues during pregnancy, has emerged as a potential therapeutic target to control allograft rejection. We demonstrate here that the level of soluble HLA‐G dimer was higher in a group of 90 patients with a functioning renal allograft compared with 40 patients who rejected (RJ) their transplants. The HLA‐G dimer level was not affected by demographic status. One of the potential mechanisms in tissue‐organ allograft rejection involves the induction of granzymes and perforin, which are the main effector molecules expressed by CD8+ cytotoxic T lymphocytes and function to destroy allogeneic transplants. Using genomics and molecular and cellular analyses of cells from T‐cell–mediated RJ and nonrejected kidney transplant patients, cells from leukocyte Ig‐like receptor B1 (LILRB1) transgenic mice, humanized mice, and genetically engineered HLA‐G dimer, we demonstrated a novel mechanism by which HLA‐G dimer inhibits activation and cytotoxic capabilities of human CD8+ T cells. This mechanism implicated the down‐regulation of Granzyme B expression and the essential involvement of LILRB1. Thus, HLA‐G dimer has the potential to be a specific and effective therapy for prevention of allograft rejection and prolongation of graft survival.—Ajith, A., Portik‐Dobos, V., Nguyen‐Lefebvre, A. T., Callaway, C., Horuzsko, D. D., Kapoor, R., Zayas, C., Maenaka, K., Mulloy, L. L., Horuzsko, A. HLA‐G dimer targets Granzyme B pathway to prolong human renal allograft survival. FASEB J. 33, 5220–5236 (2019). http://www.fasebj.org