"This is the first case of crimes against humanity charged under Kenyan domestic law using the International Crimes Act and also the first criminal prosecution of electoral-related sexual violence," the director of public prosecutions (DPP) Noordin Haji said, without disclosing the numbers of police being charged.
Authorities say the charges to be placed cover rape, murder and torture and include the case of a six-month-old baby girl whose death became a symbol of police brutality during the bloody election aftermath.
The baby, Samantha Pendo, died after being beaten by police during a raid on her house as protests flared in the western city of Kisumu.
A Kenyan inquest in 2019 had found five police commanders liable for Pendo's death.
The police crackdown following that August 2017 balloting saw dozens of people killed over a four-month period.
The Kenya National Commission on Human Rights documented 94 deaths during the crisis as well as 201 cases of sexual violence and over 300 injuries -- the majority of which were attributed to security forces.
"The attacks were planned, coordinated and not random," the DPP statement said, saying various offences such as torture, rape and sexual violence "were committed by or under the authority of senior national police officers."
Kenyan police are often accused by rights groups of using excessive force and carrying out unlawful killings, especially in poor neighbourhoods.
They have also been accused in the past of running hit squads targeting those - including activists and lawyers - investigating alleged rights abuses by police.
The 2017 protests erupted after victory was declared for then president Uhuru Kenyatta, angering supporters of his rival, the veteran opposition leader Raila Odinga.
The result was annulled by the Supreme Court after a challenge by Odinga, but he boycotted the rerun which was won by Kenyatta.
According to Missing Voices, a campaign group focused on extrajudicial killings in Kenya, there have been 1,264 deaths at the hands of police since it began collecting data in 2017.