Located on the western coast of central Africa and south of the Congo River (formerly known as the Zaire River), the kingdom arose in the late 14th century CE following the alliance of several local principalities which had been in existence since the second half of the first millennium CE. Kongo, dominated by Bantu-speaking peoples, had its capital at Mbanza Kongo - known to the Kongolese as Banza, meaning 'residence of the king' - which was located on a fertile and well-watered plateau just below the western end of the Congo River. The kingdom expanded its territory further by a gradual process of military conquest, probably motivated above all by a desire to acquire slaves. At its peak in the 15th and 16th century CE, the kingdom controlled some 240 km (150 miles) of the coast from the Congo River in the north to just short of the Cuanza River in the south, and spread some 400 km (250 miles) into the interior of central Africa up to the Kwango River.

The kingdom of Kongo, with a population of well over 2 million people at its peak, prospered thanks to trade in ivory, copper, salt, cattle hides, and slaves. The latter trade was especially lucrative and well-regulated, with rotating markets appearing in towns on fixed days of the week selling slaves acquired from the upper reaches of the Congo River. In addition to acquiring goods from elsewhere, the kingdom produced its own goods via specialized groups of craftworkers such as weavers (who produced the famous raffia fabrics of Kongo), potters, and metalworkers.

The level of trade conducted between the forest and grassland peoples of west-central Africa is indicated by the established use of a shell currency, the spiral nzimbu shells which originally came from Luanda, an offshore island located some 240 km away. Initially used as a means of storing wealth and as a standard measure of the value of other goods, the shells came to be used like coins to pay for goods and labour. Not having the region's trade all to itself, rival equatorial African kingdoms included Loango and Tio, both located to the north of Kongo, and the loose confederation of tribes of Ndongo to the south (modern Angola).

The kingdom of Kongo was highly centralised and ruled by a single monarch or nkani who appointed regional governors throughout his territory. These governors, in turn, appointed local officials and collected tribute such as ivory, millet, palm wine, and leopard and lion skins from local chiefs, which were passed on to the king at Mbanza Kongo. Tributes were paid at lavish annual ceremonies which involved much feasting and beer-drinking. In return for their offerings, chiefs and officials received the king's favour, military protection, and some material rewards such as food delicacies and clothing. There was, too, a certain religious aspect to tribute payment as it was considered a way to maintain divine favour as well as a royal one.

Kongo kings were distinguished by their symbols of office which included a headdress, royal stool, a drum, and regalia jewellery made from copper and ivory. To enforce their rule, the king controlled a standing army composed of slaves; the force in late 16th century CE numbered 16,000-20,000 men. The king was regarded as a direct link to the spiritual world, a guardian on earth who would protect the people from such calamities as disease and famine. One of the king's titles was nzambi mpungu meaning 'superior spirit' or 'supreme creator', although he himself was not regarded as sacred, only his office. To reinforce this belief, kings married descendants of a celebrated shrine guardian, the mani kabunga, who had maintained the shrine of that name since long before the Kingdom of Kongo had been established.

At a more temporal level, the king was advised by a council of a dozen or so elders composed of high-ranking members of the aristocracy (the mwisikongo) which dominated Kongo society. The aristocrats belonged to various family groups of ancient lineage and their wealth was largely derived from trade as the presence of the tsetse fly in the region precluded the breeding of cattle on a large scale and the area was so sparsely populated that land ownership had no meaning. Key positions in the centralised government included the tax officer and his staff, the chief of justice, head of the police, and official in charge of the messenger service. The rest of society was made up of the free or babuta (craftworkers and farmers) and the unfree or babika (slaves who were war captives or those unable to pay their debts).