In the elections to the Welsh Assembly on 5 May 2016 Williams retained her Brecon and Radnorshire seat with an increased majority. However, as the sole Liberal Democrat representative in the new Assembly, she stood down as leader of the Welsh Liberal Democrats the day after the election. On the first day of plenary she voted with the Government on the appointment of the First Minister. First Minister Carwyn Jones appointed her to the Welsh Cabinet as Education Secretary; 31 seats are needed for a majority in the Welsh Assembly, Labour had 29, so Williams joining with the Labour administration created a working majority.