Sierra Leone first became inhabited by indigenous African peoples at least 2,500 years ago.The Limba were the first tribe known to inhabit Sierra Leone. The dense tropical rainforest partially isolated the region from other West African cultures, and it became a refuge for peoples escaping violence and jihads. Sierra Leone was named by Portuguese explorer Pedro de Sintra, who mapped the region in 1462. The Freetown estuary provided a good natural harbour for ships to shelter and replenish drinking water, and gained more international attention as coastal and trans-Atlantic trade supplanted trans-Saharan trade.

In the mid-16th century, the Mane people invaded, subjugated nearly all of the indigenous coastal peoples, and militarised Sierra Leone. The Mane soon blended with the local populations and the various chiefdoms and kingdoms remained in a continual state of conflict, with many captives sold to European slave-traders. The Atlantic slave trade had a significant impact on Sierra Leone, as this trade flourished in the 17th and 18th centuries, and later as a centre of anti-slavery efforts when the trade was abolished in 1807. British abolitionists had organised a colony for Black Loyalists at Freetown, and this became the capital of British West Africa. A naval squadron was based there to intercept slave ships, and the colony quickly grew as liberated Africans were released, joined by West Indian and African soldiers who had fought for Britain in the Napoleonic Wars. The descendants of the black settlers were collectively referred to as the Creoles or Krios.