The Trym rises near Filton a northeast suburb of Bristol. It runs mostly underground until it gets to Southmead. It then flows towards Henleaze. The river then runs through an underground channel to the village of Westbury-on-Trym.

The Trym is then underground again and re-emerges near Henbury Golf Club before entering Blaise Castle where it is joined on the right bank by the hazel Brook. The river then flows through to Sea Mills and joins the River Avon.