Background/Objectives: Orthodontic mini-implants have become an essential source of temporary skeletal anchorage because of their versatility, minimal invasiveness, and reduced dependence on patient compliance. However, their clinical success relies on maintaining adequate primary and secondary stability throughout orthodontic treatment. Photobiomodulation (PBM) with diode lasers has been proposed as a non-invasive adjunctive therapy capable of enhancing bone healing and remodeling, thereby improving mini-implant stability. Despite encouraging findings, the available evidence remains limited and heterogeneous. The objective was to systematically evaluate the effect of diode laser photobiomodulation on the stability of orthodontic mini-implants. Methods: A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search was conducted in the PubMed, EBSCO, Scopus, and ScienceDirect databases to identify randomized clinical trials published in the last 10 years. Five randomized controlled trials involving 89 participants and 178 orthodontic mini-implants fulfilled the eligibility criteria. Mini-implant stability was assessed using objective methods, including resonance frequency analysis (ISQ) and Periotest values, while one study also evaluated insertion and removal torque. The methodological quality of the included studies was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool, and the certainty of the evidence was evaluated using the GRADE approach. Results: Three of the five included studies reported improvements in orthodontic mini-implant stability following diode laser photobiomodulation, whereas two studies found no significant differences compared with the control group. Considerable heterogeneity was identified regarding laser wavelength (618–940 nm), irradiation protocols, energy parameters, timing of force application, and stability assessment methods. Most studies presented a low risk of bias, although some concerns remained regarding allocation concealment and blinding. According to the GRADE assessment, the overall certainty of the evidence was considered moderate, mainly because of inconsistency across studies and methodological heterogeneity. Conclusions: Current evidence suggests that diode laser photobiomodulation may improve the stability of orthodontic mini-implants. Nevertheless, the small number of randomized clinical trials and the substantial variability in PBM protocols and outcome assessment methods preclude definitive clinical recommendations. Future well-designed randomized controlled trials using standardized irradiation parameters and uniform stability assessment methods are required to establish evidence-based clinical protocols.