The 2018–19 Welsh Football League Division One (known as the Nathaniel Cars Welsh Football League Division One for sponsorship reasons) was the 2018–19 season of the top football league in South Wales. The champions at the end of the season were Penybont. Together with its North Wales counterpart, the Cymru Alliance, the 16-team division formed the second tier of the Welsh football league system, one level below the nationwide Welsh Premier League. The season began on 10 August 2018 and concluded in April 2019.