The 54-year old who briefly ruled the small nation as head of a military government in 1996, will replace outgoing President Ernest Bai Koroma who cannot seek re-election due to term limits.
Before the announcement of the results, Kamura had a slim lead in the partial results.
The electoral commission had to interrupt the ballot count after a dispute over the method of tallying results left votes from 11,000 polling stations across the country uncounted.
AFP reported that Kamara supporters marched in Freetown Wednesday evening, tearing down Bio posters and alleging "foreign meddling" in the vote.
Maada Bio's supporters began celebrating in the streets of the capital Freetown on Wednesday evening in anticipation of the official announcement of results, amid calls to remain calm.
The polls which were largely peaceful has brought relief to the West African nation that was hit by Ebola epidemic in 2014-15 and endured a bloody civil war in the 1990s.