The Alyn and Deeside by-election, 2018 is a by-election that will take place in the National Assembly for Wales constituency of Alyn and Deeside on Tuesday 6 February 2018,[1] following the death of incumbent Labour AM Carl Sargeant on 7 November 2017.[2][3]

The election will be the fourth Assembly by-election to be held since its formation in 1999. The seat is a safe seat for the Labour Party, having been held continuously by the party since the beginning of devolved government. The corresponding seat in the UK Parliament has been held by Labour since its creation in 1983. As a result of the vacancy, the governing coalition of Labour, one Liberal Democrat and one Independent hold 30 of the seats in the Welsh Assembly, with the opposition holding 29.