In the elections for the National Assembly for Wales on 5 May 2016, he was elected as a Member of the National Assembly for Wales for the Mid and West Wales Region, one of seven UKIP candidates to win a seat through the Regional List system. On 10 May 2016, UKIP's AMs voted him their leader in the Welsh Assembly, defeating Nathan Gill. The UKIP leader, Nigel Farage, criticised the move as an "unjust act of deep ingratitude". Hamilton dismissed Farage's criticism as "irrelevant", accused him of "throwing toys out of pram" and referred to him as "the MEP for the South East of England". In leaked emails, he was accused by UKIP's biggest donor, Arron Banks, of being a "corrupt old Tory". Nathan Gill subsequently left the UKIP group in the assembly to sit as an independent, resulting in Neil Hamilton becoming UKIP's Leader in Wales in September 2016. Hamilton was ousted as leader of UKIP in the National Assembly on 17 May 2018 and was replaced by Caroline Jones.