The Independent Office for Police Conduct (IOPC) announced the move in a statement released on Friday evening. It said the body’s investigation into the 24-year-old’s fatal shooting has “entered a new phase”.
“Following our review of the evidence gathered so far, the Independent Office for Police Conduct (IOPC) has launched a homicide investigation into Mr Kaba’s death,” it said.
The IOPC said Mr Kaba died after a single shot was fired by a Met officer from the specialist firearms command while police attempted to “stop and contain” the vehicle he was driving.
The statement added: “This followed the activation of an automatic number plate recognition camera which indicated the vehicle was linked to a firearms incident in previous days. The vehicle Mr Kaba was driving was not registered to him.
“Our investigation team is continuing to gather and review a large amount of evidence, however as this is now a criminal investigation, we are limited in what further information we can provide. The launch of a criminal investigation does not mean that criminal charges will necessarily follow.
“We have notified Mr Kaba’s family of this latest development.
“We continue to ask that people avoid speculating about this incident out of respect for Mr Kaba’s family and for everyone else affected.”
Mr Kaba, who was due to become a father within months, died following a pursuit that ended in Streatham Hill, on Monday night.
His Audi was hemmed in by two police cars in narrow residential street Kirkstall Gardens before one round was fired from a police weapon.
CPR was administered immediately by officers at the scene and Mr Kaba was taken to hospital where he died later in the night, the IOPC earlier confirmed.
A detailed search was completed on Tuesday night and no non-police issue firearm was found in the vehicle or at the scene, the IOPC said.
It is understood the only gun recovered from the scene was the one involved in the incident.
Mr Kaba's family earlier questioned whether his life would have been "cut short" if he were not black - as they demanded a murder investigation into his death.
In a statement issued shortly before 8pm, Met Assistant Commissioner Amanda Pearson said her “thoughts and sympathies remain with Mr Kaba’s friends and family” following the announcement that an officer is the subject of a homicide probe.
“I also know how concerned our communities are and how they will also be affected by this significant update. We share their concern.
“The Met is co-operating fully as the IOPC work to independently establish the full circumstances surrounding the shooting.”
She said officer is not currently on operational duties. “A senior officer will now carefully consider their work status going forward,” she said.
Ms Pearson continued: “I absolutely understand that this shooting is a matter of grave concern, particularly for our Black communities.
“I also know what a difficult and often dangerous job firearms officers in particular do every day to try to protect the public. They understand and expect that on the very rare occasions they discharge their weapons they will face intense scrutiny. I don’t underestimate the impact on them of this development.
“I’d urge the public to allow the IOPC the time and space needed to progress the investigation.”
Mr Kaba’s family said on Wednesday they were "devastated" and needed "answers and accountability" over his death.
In a statement released through the charity Inquest, they said: "The family of Chris Kaba seek a homicide investigation into his death from the outset.
"We have today told the Independent Office for Police Conduct (IOPC) of that demand and that we do not want any delay as has happened in other fatal shootings - otherwise we and the wider public can have no confidence that the police will be held to account.
"We also want the IOPC to tell us whether or not a weapon was found in any search of the vehicle that Chris was driving. We have not received this information even though the shooting happened almost two days ago.
"Finally, we are desperately appealing for any witnesses, whether before, during or after the pursuit and the shooting to come forward to the IOPC and/or to our solicitors at Hickman and Rose.
"We are devastated; we need answers and we need accountability. We are worried that if Chris had not been black, he would have been arrested on Monday evening and not had his life cut short."
The Metropolitan Police earlier expressed its condolences to Mr Kaba's loved ones, saying the force understood that "the family and community want answers".
In a statement issued earlier on Wednesday, Commander Alexis Boon said the incident was "extremely concerning" and vowed the force would co-operate with the police watchdog in its aftermath.
The officer said: "I would like to express my sincere condolences to the family and friends of the man who died and I recognise the devastating and lasting impact this tragic incident will have on them.
"I understand that this incident is extremely concerning and I would like to reassure the community that the Met is co-operating fully with the Independent Office for Police Conduct (IOPC) as they carry out a thorough and independent investigation."
Prosper Kaba, Mr Kaba's father, told BBC News: "Really we are shocked to see that in this century from a specialist of the law like police, can shortcut someone's life, especially a young boy."