The McLennan River originates in the Premier Range, flowing from McLennan Glacier between Mount Stanley Baldwin and Mount Arthur Meighen. The river flows east out of the mountains into the Rocky Mountain Trench near Valemount. Then it turns northwest, flowing through the Rocky Mountain Trench, picking up tributary streams flowing from the Selwyn Range to the east and the Premier Range to the west. It joins the Fraser River at Tête Jaune Cache.