The New York organization said in a newly released report that bringing perpetrators to justice would help stabilize the African nation.
The 81-page report, titled "Ballots to Bullets: Organized Political Violence and Kenya's Crisis of Governance," outlines how hundreds of Kenyans were killed amidst violence after the December 2007 presidential elections.
The report, among other things, accuses Kenyan police of using excessive force in responding to demonstrations, killing hundreds of people.
"For the new government to function well and earn the people's trust, it needs to first heal the wounds by prosecuting those behind the violence," said Georgette Gagnon, Africa director at Human Rights Watch.
"Inciting violence along ethnic lines almost destroyed Kenya. The new government now has a chance to repair those fractures."
In all, the group said the post-election violence left more than 1,000 people dead and 500,000 people displaced from their homes.