The leaflets of lupinus succulentus
are quite distinctive, being unusually wide towards the tips, hairless, and thick, almost succulent-like, reflecting the fact that this species favors soils with a high water content. Leaves grow on stalks that are 2 or 3 times as long as the leaflets. Plants can grow large, over 3 feet tall, often forming extensive clumps.
The inflorescence is a vertical cluster of whorled flowers, occupying up to 6 inches along the top of the stem. Calyces and flower stalks have a very light covering of short hairs. The two calyx lips are approximately equal in size, and the upper is divided into two lobes. Buds are pale greenish yellow, while the flowers are usually bluish-purple, becoming darker as they mature, but can also be pinkish or nearly white. The center of the banner petal is white, flecked by dark dots. The upper and lower margins of the keel petals are lightly hairy.