Yucca Thompsoniana has a trunk up to 1 m tall, branching above the ground. Leaves are narrow and dagger-like, a bit glaucous, up to 35 cm long and 10 mm wide.
It flowers before there is any trunk at all, but continues to flower after the stem begins to grow. Inflorescence is a panicle about 100 cm high. Flowers are white, about 4 cm long. Fruit is a dry, egg-shaped capsule.