Lying entirely in the Eastman Region, it runs from the U.S. border (where it meets with Minnesota State Highway 313) to a dead end in Grand Beach.

PTH 12 forms the Manitoba section of MOM's Way, a tourist route from Thunder Bay to Winnipeg.

[2] PTH 12 begins in the southeast corner of the province in the Rural Municipality of Piney as a continuation of Minnesota State Highway 313 (MN 313) at the Warroad-Sprague Border Crossing.

Between the U.S. border and Buffalo Point Road, the highway lies less than 5 kilometres (3.1 mi) from the shores of Lake of the Woods.

The highway enters woodlands again to have an intersection with PR 210 near Menisino before curving northwest to cross into the Rural Municipality of Stuartburn.

The highway has a short concurrency (overlap) with PR 311 in Blumenort, which it bypasses along its eastern side, before crossing into the Rural Municipality of Ste.

It now has a rather large Cloverleaf interchange with PTH 1 (Trans-Canada Highway) before narrowing to two lanes as it enters the Rural Municipality of Tache.

Provincial Road 310 (PR 310) is a short 4-kilometre-long (2.5 mi) north-south spur in the Rural Municipality of Piney, connecting PTH 12 at South Junction south to the Roseau-South Junction Border Crossing, which in turn provides a connection to the town of Roseau, Minnesota.