Adults with congenital heart disease (ACHD) represent a rapidly growing patient population that is uniquely predisposed to rhythm disturbances. Arrhythmia mechanisms are shaped by congenital anatomy, prior surgical repairs, and progressive chamber remodeling, necessitating lesion-specific strategies. Intra-atrial reentrant tachycardia remains the dominant atrial rhythm disturbance in repaired or surgically modified atria, whereas atrial fibrillation is increasingly encountered with advancing age. While pulmonary vein isolation using pulsed field ablation has entered clinical practice, extra-pulmonary triggers and extensive atrial disease pose unique challenges in ACHD. Ventricular tachycardia in repaired tetralogy of Fallot predominantly arises from slow-conducting anatomical isthmuses. Ongoing studies are evaluating whether preventive isthmus ablation at the time of pulmonary valve replacement reduces subsequent arrhythmic risk. Intraoperative conduction mapping has emerged as a powerful tool to identify the His-Purkinje system in real-time during congenital surgery, reducing postoperative atrioventricular block. Device therapy is evolving toward conduction system pacing as a physiologic strategy across a broader spectrum of congenital heart disease subtypes, along with selective use of subcutaneous defibrillators and leadless devices. Risk prediction and sudden death prevention are being refined by the integration of genetics, application of artificial intelligence, and personalized digital twin models. Together, these innovations herald a future of substrate-guided and mechanism-based arrhythmia management in ACHD. This review synthesizes the evidence underpinning these advances, outlines their clinical applications, and identifies priorities for future research aimed at reducing arrhythmia burden, sudden death risk, and long-term morbidity in this complex population.