The long, low, “rectangular” body, coupled with a muscular and rather massive physique, allows the Sussex to penetrate dense cover when hunting. Its movement is deliberate and rolling because of its short legs and comparatively wide body, a gait that emphasizes power over speed. The abundant body coat is flat or slightly wavy, giving protection from thorns. A distinctive feature is the long feather between the toes, which should be long enough to cover the toenails. The expression is somber and serious, even frowning, but the wagging tail belies its true nature. The Sussex tends to bark when hunting, which helps the hunter locate it in thick cover.

The Sussex spaniel tends to be less playful and demonstrative than other spaniels, with a lower energy level. This makes it better suited for city life, but it still appreciates the chance to take to the wilds and hunt up birds. It tends to bark when hunting, which has made it less popular with hunters than other breeds; some also bark or howl when not hunting. At home it is calm, steady and easygoing, although it may be aggressive to strange dogs. Its somber expression is misleading because it is quite cheerful.