Abstract Background: Lumbar facet joint arthropathy (LFJA) is a major cause of low back pain (LBP), with current treatments offering limited long-term benefits. Bone marrow–derived mesenchymal stem cells (BM-MSCs) show promise due to their immunomodulatory and trophic effects, potentially addressing underlying degenerative processes in LFJA. Objectives: This initial report describes the outcomes of the first treated patient in an ongoing mutidisciplinary phase 1 clinical trial evaluating the safety and feasibility of intra-articular allogeneic BM-MSCs for painful LFJA. Methods: Following enrollment in our IRB-approved protocol, symptomatic LFJA was confirmed through double blocks on L4 and L5 medial branches. Two 1-mL syringes, each containing 10 million BM-MSCs, were prepared in the cGMP facility and administered bilaterally to the patient’s L4-L5 lumbar facet joints. The patient underwent standardized follow-ups, including clinical examinations and functional and imaging assessments for 2 years, utilizing patient-reported outcomes measurement information system—computer adaptive tests (PROMIS CATs), visual analogue scale, Oswestry disability index, work functional status and opioid pain medication use, and MR imaging Fenton–Czervionke score. Results: The patient tolerated the procedure well, with no drug-related adverse events during the study period. Pain, spine function, and work functional status improved at multiple follow-ups. This patient also reported improvements in mental and social health, along with a notable improvement in the grade of facet synovitis observed at the one-year follow-up MRI evaluation. Conclusions: This case report suggests the safety and feasibility of administering intra-articular allogeneic BM-MSCs, offering therapeutic benefits for pain management and functional activities.