Background and PurposeThe KCNQ2 gene encodes for the K_v7.2 subunit of non‐inactivating potassium channels. KCNQ2‐related diseases range from autosomal dominant neonatal self‐limited epilepsy, often caused by KCNQ2 haploinsufficiency, to severe encephalopathies caused by KCNQ2 missense variants. In vivo and in vitro effects of the sodium channel blocker eslicarbazepine acetate (ESL) and eslicarbazepine metabolite (S‐Lic) in a mouse model of self‐limited neonatal epilepsy as a first attempt to assess the utility of ESL in the KCNQ2 disease spectrum was investigated.Experimental ApproachEffects of S‐Lic on in vitro physiological and pathological hippocampal neuronal activity in slices from mice carrying a heterozygous deletion of Kcnq2 (Kcnq2^+/−) and Kcnq2^+/+ mice were investigated. ESL in vivo efficacy was investigated in the 6‐Hz psychomotor seizure model in both Kcnq2^+/− and Kcnq2^+/+ mice.Key ResultsS‐Lic increased the amplitude and decreased the incidence of physiological sharp wave–ripples in a concentration‐dependent manner and slightly decreased gamma oscillations frequency. 4‐Aminopyridine‐evoked seizure‐like events were blocked at high S‐Lic concentrations and substantially reduced in incidence at lower concentrations. These results were not different in Kcnq2^+/+ and Kcnq2^+/− mice, although the EC₅₀ estimation implicated higher efficacy in Kcnq2^+/−animals. In vivo, Kcnq2^+/− mice had a lower seizure threshold than Kcnq2^+/+ mice. In both genotypes, ESL dose‐dependently displayed protection against seizures.Conclusions and ImplicationsS‐Lic slightly modulates hippocampal oscillations and blocks epileptic activity in vitro and in vivo. Our results suggest that the increased excitability in Kcnq2^+/− mice is effectively targeted by S‐Lic high concentrations, presumably by blocking diverse sodium channel subtypes.