Soyo was formerly known as São António do Zaire, a Portuguese colonial name that reflects the town's centuries of history as a port at the mouth of the Congo. The area was part of the Kingdom of Kongo long before Portuguese contact, and the estuary has been a place of trade and movement for at least five hundred years.
Some remnants of the colonial-era town survive — older buildings, a church, and the general layout of the original settlement. The town saw heavy fighting during the Angolan Civil War and bears marks from that period as well. Walking through the older parts of Soyo gives some sense of the layered history, though the oil industry has transformed much of the original character.