24-year-old Cliff Mitchell has also been found guilty of one count of kidnap and a breach of a non-molestation order.
He was a serving PC in Hounslow when a number of the offences were committed.
Mitchell was dismissed from the Met in December and will be sentenced at a later date.
Deputy Assistant Commissioner Stuart Cundy said: “This is a truly shocking case and I am sickened by Mitchell’s abhorrent behaviour and the pain he has caused the victims, who have shown enormous bravery by coming forward and giving evidence in court.
“It is down to their courage that he has been convicted and faces a significant custodial sentence. I would also like to recognise the brave member of the public who came to the aid of one of the victims as she ran from Mitchell’s car.
“Mitchell not only carried out a sustained campaign of abuse against both of his victims, but he told one of them she would never be believed due to the fact he was a police officer. This brazen abuse of power makes Mitchell’s actions all the more deplorable.
“I know this is another case which will impact the confidence people have in us. We are doing more than we have done in decades to rid the Met of those who corrupt our integrity, including investing millions of pounds into our professional standards team and bringing in additional officers and staff with specialist skills and experience to investigate criminality and misconduct.
“Part of that is dismissing officers who should not be here at the earliest opportunity. Mitchell was dismissed from the Met in December, we did not wait for his conviction today.”
On Tuesday, the 5th of September last year, Mitchell attended the address of a woman who he raped at knifepoint before blindfolding her with his hooded top, tying her hands with cable ties and forcing her into his car.
In Longfield Avenue in Hackbridge, she managed to escape from the vehicle and approached a member of the public who let her into her car before calling 999.
An alert was put out for Mitchell’s car and he was stopped and arrested around seven miles away in Putney.
An investigation was launched, led by the Met’s dedicated Domestic Abuse and Sexual Offending (DASO) team.
DASO was set up as part of the Met’s “ongoing efforts to tackle violence against women and girls, with more than 50 experienced investigators targeting any officer or staff member suspected of domestic abuse or sexual offences.”
Officers from the team searched Mitchell’s car and recovered the hooded top.
A search of an address linked to Mitchell found a bag containing cable ties, similar to those the victim had described as being used around her wrists.
Mitchell was remanded in custody and charged with multiple counts of rape, kidnap and breach of a non-molestation order and was immediately suspended.
Mitchell had previously been subject to a rape investigation in 2017, which had resulted in no further action.
Following his arrest, the case was re-investigated and a file passed to the CPS.
This resulted in Mitchell being charged with an additional three counts of rape of a child under 13 and three counts of rape.
These six charges relate to a second victim and occurred between 2014 and 2017.