Laryngeal squamous cell carcinoma (LSCC), although one of the most common head and neck cancers, has a static or slightly decreased survival rate because of difficulties in early diagnosis, lack of effective molecular targeting therapy, and severe dysfunction after radical surgical treatments. Therefore, a novel therapeutic target is crucial to increase treatment efficacy and survival rates in these patients. Glycoprotein NMB (GPNMB), whose role in LSCC remains elusive, is a type 1 transmembrane protein involved in malignant progression of various cancers, and its high expression is thought to be a poor prognostic factor. In this study, we showed that GPNMB expression levels in LSCC samples are significantly higher than those in normal tissues, and GPNMB expression is observed mostly in growth‐arrested cancer cells. Furthermore, knockdown of GPNMB reduces monolayer cellular proliferation, cellular migration, and tumorigenic growth, while GPNMB protein displays an inverse relationship with Ki‐67 levels. Therefore, we conclude that GPNMB may be an attractive target for future LSCC therapy. In the present study, we showed higher expression levels of GPNMB mRNA in all clinical stages and grades of head and neck squamous cell carcinoma (HNSCC) patients compared with normal tissues and the remarkably higher expression of GPNMB in malignant lesions compared with normal squamous epithelium in laryngeal squamous cell carcinoma (LSCC) clinical samples. Furthermore, we demonstrated the critical roles of GPNMB in 2D monolayer proliferation, cellular migration, 3D sphere growth in vitro, and xenograft tumor formation in vivo in LSCC cell lines. Additionally, we revealed the mutually exclusive expression of GPNMB and Ki‐67 within LSCC cells in the xenografted tumors and clinical samples, suggesting that GPNMB works in Ki‐67–negative, dormant cancer cells.