Before the arrival of the Slavonic peoples in the Balkans during the 6th century CE, the area now known as Montenegro was inhabited principally by the Illyrians.

During the Bronze Age, the Illirii, probably the southernmost Illyrian tribe of that time, that gave their name to the entire group were living near Skadar lake on the border of Albania and Montenegro and neighboring with the Greek tribes south. Along the seaboard of the Adriatic, the movement of peoples that was typical of the ancient Mediterranean world ensured the settlement of a mixture of colonists, traders, and those in search of territorial conquest. Substantial Greek colonies were established on the 6th and 7th centuries BCE and Celts are known to have settled there in the 4th century BCE. During the 3rd century BCE, an indigenous Illyrian kingdom emerged with its capital at Scutari. The Romans mounted several punitive expeditions against local pirates and finally conquered the Illyrian kingdom in the 2nd century BCE, annexing it to the province of Illyricum.

The division of the Roman Empire between Roman and Byzantine rule – and subsequently between the Latin and Greek churches – was marked by a line that ran northward from Shkodra through modern Montenegro, symbolizing the status of this region as a perpetual marginal zone between the economic, cultural, and political worlds of the Mediterranean. As Roman power declined, this part of the Dalmatian coast suffered from intermittent ravages by various semi-nomadic invaders, especially the Goths in the late 5th century and the Avars during the 6th century. These soon were supplanted by the Slavs, who became widely established in Dalmatia by the middle of the 7th century. Because the terrain was extremely rugged and lacked any major sources of wealth such as mineral riches, the area that is now Montenegro became a haven for residual groups of earlier settlers, including some tribes who had escaped Romanisation.