The 2012–13 Welsh Alliance League, known as the Lock Stock Welsh Alliance League for sponsorship reasons, is the 29th season of the Welsh Alliance League, which consists of two divisions: the third and fourth levels of the Welsh football pyramid.
There are fifteen teams in Division 1 and thirteen teams in Division 2, with the champions of Division 1 promoted to the Cymru Alliance and the bottom team relegated to Division 2. In Division 2, the champions, and runners-up are promoted to Division 1.
The season began on 10 August 2012 and concluded on 11 May 2013 with Caernarfon Town as Division 1 champions and Llangefni Town relegated to Division 2. In Division 2, Llandyrnog United were champions with Llanfairpwll as runners-up.
Llanfairpwll and Caernarfon Wanderers were relegated and replaced by Division 2 champions, Glantraeth and runners-up, Llanberis, who were promoted to Division 1.