The first human beings, homo erectus, evolved in the east African rift valley, within a thousand miles of Zanzibar, about 1.5 million years ago. They migrated throughout africa and later asia and beyond, becoming hunter-gatherers. Near rivers and coasts these people developed fishing techniques, and it is possible that Zanzibar's first human inhabitants were fishermen who crossed from the African mainland in dugout canoes sometime during the 1st millennium BC.

At around the same time, or even earlier, the east African coast (including the islands of Zanzibar) may have received visitors from many parts of the ancient world, such as Mesopotamia (present-day Iraq) and Egypt. The Egyptian pharaohs sent expeditions to the land they called Punt (present-day Somalia) in around 3000BC and again in 1492BC; these possibly continued southwards down the east African coast. This theory is supported by carvings on temple walls at Luxor showing sailing boats with slaves unloading gold, ivory tusks, leopard skins and trees of frankincense.

Other visitors may have included Phoenicians, a seafaring people from the eastern shores of the Mediterranean. Around 600BC, a Phoenician fleet sailed south along the coast, past Zanzibar, and is believed to have circumnavigated Africa before returning to the Mediterranean three years later.

By the 1st century AD Greek and Roman ships were sailing from the Red Sea down the east African coast, searching for valuable trade goods such as tortoiseshell, ebony and ivory. Around AD60, a Greek merchant from Alexandria wrote a guide for ships in the Indian Ocean called The Periplus of the Erythaean Sea. This is the first recorded eyewitness account of the east African coast, and describes 'the Island of Menouthesias' (most likely the present-day island of Unguja, also called Zanzibar Island) as 'flat and wooded' with 'many rivers' and 'small sewn boats used for fishing'. Another Alexandrine Greek, Claudius Ptolemaeus (usually called Ptolemy), also mentioned Menouthesias in his book Geographike, written about AD150.

At about the same time, it is thought that Arab and Persian trading ships from the Persian Gulf were also sailing down the coast of east Africa. They sailed south on the northeast monsoon between November and February, carrying beads and cloth, and even Chinese porcelain that had come via India. Then, between March and September, after the winds changed direction, they returned north on the southwest monsoon, carrying the same tortoiseshell, ebony and ivory that had attracted the Greeks and Romans, plus mangrove poles for timber and other goods. The Arabs and Persians traded with the local inhabitants but they remained visitors and, at this stage, did not settle.

During the 3rd and 4th centuries AD, other groups of migrating peoples started to arrive on the east coast of Africa. These people were Bantu (the name comes from the term used to define their group of languages); they originated from the area around present-day Cameroon in the centre of the continent, then spread throughout eastern and southern Africa. On the east African coast, they established settlements, which slowly grew into towns, and eventually became the major trading cities such as Kilwa, Lamu and Mombasa on the mainland, and Unguja Ukuu on the island of Unguja (Zanzibar Island). These coastal settlers traded with the Arabs, exporting ivory, rhino-horn, tortoiseshell and palm oil, and importing metal tools and weapons, wine and wheat.

The Arab traders called the east African coast 'Zinj el Barr', meaning 'land of the black people', from where the modern name Zanzibar is derived. 'Zinj' comes from zang, the Persian word for 'black', and barr is the Arabic word for 'land'. The Arabs may also have derived the word from Zayn za'l barr, meaning 'Fair is this land'. Zanzibar remained the name of the whole coast, including the islands of Unguja and Pemba (which together make up the present-day state of Zanzibar), until the late 15th century.