During liver and combined liver-kidney transplantation, rapid and massive shifts in potassium levels can lead to serious complications, including malignant arrhythmias, severe myocardial depression, and catecholamine-refractory cardiogenic shock. In selected high-risk cases, extracorporeal life support with veno-arterial ECMO (VA-ECMO) combined with continuous renal replacement therapy (CRRT) is proposed as a preventive measure. A 5-year-old patient with autosomal recessive polycystic kidney disease and congenital hepatic fibrosis underwent combined liver–kidney transplantation. Initial serum potassium was 6.2 mmol/L due to a previous infective peritoneal dialysis. During pre-anhepatic phase, despite optimal medical therapy, serum potassium reached 7.87 mmol/L. CRRT was instated and potassium levels normalized before reperfusion. Central VA-ECMO was established prior to graft implantation to face reperfusion after failed peripheral canulation attempt due to deterioration of myocardial function leading to hemodynamic collapse refractory to inotropes. Although Custodiol (HTK) was used as the preservation solution, a new potassium peak was reached associated with ST segment elevations, ventricular arrhythmias, and global myocardial depression. During the remainder of the procedure, VA-ECMO therapy and CRRT were used to restore hemodynamic stability and potassium levels before intensive care unit (ICU) transport. ECMO was weaned postoperatively, and the patient was discharged with satisfactory graft function. Although the use of ECMO in liver transplantation is uncommon, early application allowed treatment of potentially life-threatening hyperkalemia with CRRT and preventing hemodynamic collapse.