It is estimated to comprise 7% of the mass of the asteroid belt, and its diameter of 544 kilometres (338 mi) is slightly larger than that of 4 Vesta. It is however 10–30% less massive than Vesta, placing it third among the asteroids. It is possibly the largest irregularly shaped body in the Solar System (that is, the largest body not rounded under its own gravity), and a remnant protoplanet.

When Pallas was discovered by astronomer Heinrich Wilhelm Matthäus Olbers on March 28, 1802, it was counted as a planet, as were other asteroids in the early 19th century. The discovery of many more asteroids after 1845 eventually led to their re-classification.

The Palladian surface appears to be a silicate material; the surface spectrum and estimated density resemble carbonaceous chondrite meteorites. The Palladian orbit, at 34.8°, is unusually highly inclined to the plane of the asteroid belt, and the orbital eccentricity is nearly as large as that of Pluto, making Pallas relatively inaccessible to spacecraft.