Osteosarcoma is the most common primary malignant bone tumor in childhood. Patients who present with metastatic disease at diagnosis or relapse have a very poor prognosis, and this has not changed over the past four decades. The Wnt signaling pathway plays a role in regulating osteogenesis and is implicated in osteosarcoma pathogenesis. DKK-1 inhibits the canonical Wnt signaling pathway, causing inhibition of osteoblast differentiation and disordered bone repair. Our lab previously demonstrated that an mAb against DKK-1 prevented metastatic disease in a mouse model. This study expands upon those findings by demonstrating similar results with a small-molecule inhibitor of DKK-1, WAY262611, both in vitro and in vivo. WAY262611 was evaluated in vitro on osteosarcoma cell lines, including proliferation, caspase activation, cell-cycle analysis, and signaling pathway activation. We utilized our orthotopic implantation/amputation model of osteosarcoma metastasis in vivo to determine the impact of WAY262611 on primary tumor progression and metastatic outgrowth of disseminated tumor cells. Differentiation status was determined using single-cell RNA sequencing. We show here that WAY262611 activates canonical Wnt signaling, enhances nuclear localization and transcriptional activity of β-catenin, and slows proliferation of osteosarcoma cell lines. We also show that WAY262611 induces osteoblastic differentiation of a patient-derived xenograft of osteosarcoma in vivo, as well as inhibiting metastasis. This work credentials DKK-1 as a therapeutic target in osteosarcoma, allowing for manipulation of the Wnt signaling pathway and providing preclinical justification for the development of new biologics for the prevention of osteosarcoma metastasis.