Background <p>Lymph node metastasis is a critical determinant of poor prognosis in head and neck squamous cell carcinoma (HNSCC). Secreted phosphoprotein 1 (SPP1) has been implicated in the progression of multiple malignancies; however, its clinical relevance and potential molecular mechanisms in HNSCC remain not fully understood. This study aims to comprehensively characterize the expression profile, biological functions, and potential molecular mechanisms of SPP1 during HNSCC progression.</p> Methods <p>Public datasets were analyzed to assess SPP1 expression and its association with clinicopathological features and patient outcomes. Forty surgical specimens of head and neck squamous cell carcinoma (including adjacent normal tissues, non-metastatic tumors and lymph node metastatic tumors) were collected and verified by immunohistochemistry, quantitative PCR and Western blotting. Then, cellular functional assays including CCK-8, EdU synthesis, wound healing, and Transwell assays were performed to evaluate the effects of SPP1 knockdown and overexpression on the proliferation and invasion of head and neck squamous cell carcinoma cells. Transcriptome sequencing was performed in SPP1 knockdown cells and control cells (<i>n</i> = 3 in each group), followed by differential expression analysis, enrichment analysis, and gene set enrichment analysis to explore potential mechanisms.</p> Results <p>The results showed that SPP1 expression was significantly increased in HNSCC tissues compared with adjacent normal tissues and was associated with lymph node metastasis, advanced tumor stage, and poor prognosis. Experimental validation in clinical samples confirmed that SPP1 expression was increased in tumors, especially in cases with lymph node metastasis. The results of the cell function experiments showed that the knockout of the SPP1 gene significantly inhibited the proliferation and migration abilities of HNSCC, while when the SPP1 gene was overexpressed, these functions of the cells were enhanced. Transcriptomic profiling identified 1,853 differentially expressed genes following SPP1 knockdown, with enrichment in pathways related to extracellular matrix organization, focal adhesion, and oncogenic signaling. Gene set enrichment analysis further supported the involvement of extracellular matrix remodeling and migration-related biological processes.</p> Conclusions <p>SPP1 promotes the malignant progression of HNSCC and is closely associated with lymph node metastasis. Its tumor-promoting effects may be mediated, at least in part, through regulation of extracellular matrix- and adhesion-related signaling pathways. These findings highlight SPP1 as a potential biomarker and therapeutic target in HNSCC.</p>