Background/Objectives: Radiation-induced laryngeal radionecrosis and chondroradionecrosis (LRN/LCRN) are uncommon but potentially severe complications of radiotherapy that may lead to airway compromise, persistent functional impairment, or total laryngectomy. This systematic review evaluated the available evidence on hyperbaric oxygen treatment (HBO₂) for established LRN/LCRN, with emphasis on laryngeal preservation, clinical response, functional outcomes, and adverse events. Methods: PubMed, Embase, Scopus, and the Cochrane Library were searched from inception to 8 August 2026, with additional reference and citation searching. Original human studies reporting therapeutic HBO₂ for established LRN/LCRN were included. Two reviewers independently screened studies, extracted data, and performed design-specific Joanna Briggs Institute critical appraisal. Owing to substantial clinical and methodological heterogeneity, findings were synthesized narratively without meta-analysis. Results: Twenty reports were included, predominantly case reports, small case series, and retrospective observational studies. No randomized trial specifically evaluating HBO₂ for LRN/LCRN was identified. Disease severity, treatment regimens, co-interventions, follow-up duration, and outcome definitions varied substantially. Clinical improvement and laryngeal preservation were reported in selected patients, but functional recovery was inconsistent, with persistent tracheostomy dependence documented despite anatomical preservation. Adverse-event reporting was incomplete. Conclusions: Clinical improvement and laryngeal preservation were reported following care that included HBO₂. However, the available evidence cannot distinguish its independent contribution from concomitant treatments and patient selection. Laryngeal preservation does not always translate into functional recovery, highlighting the need for prospective multicenter studies with standardized diagnostic, treatment, and functional outcomes.