No team was relegated from Division 2 as Meliden resigned from the Welsh Alliance League at the end of the season.
Conwy Borough were champions in the previous season and were promoted to the Cymru Alliance.
The bottom two teams from the previous season, Pwllheli and Trearddur Bay, were relegated to Division 2 for 2018–19.
[3] Division 2 champions, Prestatyn Sports and runners-up, Bodedern Athletic were promoted in their place.
Prestatyn Sports were champions in the previous season and were promoted to Division 1 along with runners-up, Bodedern Athletic.