Background: Thermal ablation techniques have been proposed as minimally invasive alternatives to surgery for early-stage breast cancer (BC), with the potential to reduce treatment burden while preserving oncological outcomes. The aim of this review was to evaluate the available evidence on the effectiveness and safety of thermal ablation techniques in patients with early-stage BC. Methods: We conducted a systematic review and narrative synthesis in accordance with PRISMA guidelines. MEDLINE, Embase, the Cochrane Library, and the INAHTA database were searched for studies published between 2014 January and 2026 May. Eligible studies included randomised controlled trials, non-randomised comparative studies, and prospective single-arm studies enrolling adult patients with early-stage BC treated with cryoablation (CYA), microwave ablation (MWA), radiofrequency ablation (RFA), high-intensity focused ultrasound ablation (HIFU), or laser ablation (LA), with or without standard care. Risk of bias was assessed using RoB 2.0 and ROBINS-I, and certainty of evidence was evaluated using GRADE. Results: Twenty-two trials (in 24 publications) were included: twelve on CYA, five on MWA, three on RFA, two on HIFU, and one on LA, with one trial evaluating both CYA and MWA. Comparative evidence was available for CYA, MWA, and RFA, while HIFU and LA were evaluated exclusively in single-arm studies. Across interventions, recurrence rates were generally low, overall survival was high, reported adverse events were predominantly mild to moderate. Most studies were small, had short follow-up, and frequently included post-ablation surgical resection, limiting causal attribution. Certainty of evidence ranged from very low to moderate, depending on intervention and outcome. Conclusion: Thermal ablation techniques demonstrate favourable short-term safety profiles and promising oncological outcomes in selected patients with early-stage BC. Current evidence is limited by low certainty, heterogeneous study methodologies, and limited long-term comparative data. High-quality comparative studies with standardised assessment methods and long-term follow-up are required to elucidate the comparative clinical evidence of thermal ablation techniques and inform their role in routine clinical practice.