Approximately 21 mi (34 km) long, it flows through a historically important coal-producing region north of Pittsburgh.

[4] It flows generally south, past West Pittsburg and Homewood, then receives Connoquenessing Creek west of Ellwood City and flows past Beaver Falls and New Brighton.

It joins the Ohio at Bridgewater and Rochester (flowing between those towns) at the downstream end of a sharp bend in the Ohio approximately 20 mi (32 km) northwest of (and downstream from) Pittsburgh.

In the lower reaches near the Ohio River, the Beaver cuts through a gorge of underlying sandstone.

The river itself was either named for King Beaver (Tamaqua) of the Delaware nation that had migrated to the area in the late 1740s, or for the animal.