Kamara's All People's Congress (APC) party elected him to run again in the next presidential election on June 24, in which incumbent Julius Maada Bio will seek to win a second term.
Kamara narrowly lost to then opposition candidate Maada Bio in 2018.
"The work has just begun... I appeal to all to bury the hatchet, avoid backbiting and work as a team", Kamara said at a crowded APC party headquarters in the city of Makeni after he won with 85% of votes against 17 other candidates.
"One of our key objectives is to work together for peace within the party... Nobody is an enemy," he said.
Sierra Leone's anti-corruption commission indicted him on corruption allegations in 2021, when he was foreign minister, along with five other officials.
The six are charged with various counts of corruption involving $4.2 million meant for the renovation of Sierra Leone's chancery building in Manhattan.
Kamara himself is charged with two counts including misappropriation of public funds amounting to $2,560,000 meant for the chancery building's reconstruction.
The trial is ongoing and he has denied wrongdoing.