Stephen Cooperwhite, 35, subjected the two females to a series of sexual assaults dating back to September 2002.
The High Court in Edinburgh heard how Cooperwhite attacked the women at addresses in the Hebrides and Stirlingshire.
Cooperwhite, who quit his Central Scotland Police job late last year, used physical force to get his way with his terrified victims.
He ignored their pleas for him to stop and carried on abusing them, the court heard.
He was caught after the policewoman he abused told her bosses what had happened.
Detectives at the force launched an investigation and discovered Cooperwhite had also abused another woman.
He was arrested in August 2010 as he was completing his basic training at the Scottish Police college in Tulliallan, Fife.
The court heard that while he attended the college he was rumoured to be cheating on his partner with another officer.
Cooperwhite denied the rape charges and claimed his victims were "bunny boilers" who had told lies about him.
But a jury of eight men and seven women refused to believe he was the victim to a complicated criminal conspiracy.
The jury returned verdicts of guilty on two charges of rape against Cooperwhite, of Paisley, Renfrewshire.
Judge John Beckett, QC, told the first offender that he would be remanded in custody and sentence would be deferred to the High Court in Glasgow on March 22.
Cooperwhite's mother wept as she saw her son being led down the stairs to begin his spell in prison. His father shouted: "Love you."
The court was told how Cooperwhite physically assaulted one woman at an address on the island of Benbecula.
The 34-year-old victim said: "I tried to push him away, but he wouldn't stop. He grabbed me on the arms tightly. He hit me against the kitchen door. He was strong – it was quite an overwhelming feeling.
"He punched me on the side of the face. I was shocked. It was horrifying."
Several years later, after he joined Central Scotland Police, Cooperwhite targeted a female colleague and repeatedly attacked her at an address in Stirlingshire.
The WPC told the court she was shocked and horrified about what had happened. She said she felt unable to concentrate on her work and her performance had suffered.
She told prosecution advocate Tim Niven Smith: "I was depressed. I was very emotional. I confided in colleagues about what happened."
Detectives investigated Cooperwhite and were able to establish that he had abused the other woman.
Cooperwhite was eventually charged with rape by Central Scotland Police officers.
During cross-examination at his trial, Cooperwhite told Mr Niven Smith he thought his second victim had made up the rape allegations because she wasn't a competent police officer.
He added: "She was under pressure at work."
He also told Mr Niven Smith he thought his two victims were "bunny boilers" who had lied in court against him.
When the jury returned guilty verdicts, Cooperwhite shook his head in disbelief and started to cry. His family, who came to court each day, also wept.
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