Mohammed Ali Abboud said he was attacked by Agnieszka Szefler in January 2015 at his Bridge of Earn home and acted in self defence.
However, a jury rejected the claims and found him guilty of inflicting 19 knife wounds on the 27-year-old teacher.
Judge Lord Uist urged Abboud to tell the truth about why he took her life.
Following a seven-day trial, the jury at the High Court in Edinburgh took two-and-a-half hours to return a verdict of guilty of murder.
They also returned a guilty verdict to a charge that Abboud attempted to defeat the ends of justice and had taken active steps to avoid arrest by tampering with evidence.
Lord Uist told Abboud he would defer sentence for the court to obtain reports about his character.
He added: "The crime of which you have been convicted of can only result in one sentence - life imprisonment.
"However, I cannot sentence you at this time as you are a first offender. I am required by law to obtain a criminal justice and social work report.
"I hope that when the reporter speaks to you, you will reveal what happened in the house on 23 January 2015 when you inflicted those injuries on Agnieszka Szefler."
During the trial, the court heard that Abboud and Ms Agnieszka had been in a long-term relationship, but the pair split after she took a job in Kuwait.
Jurors were told she had come back to Scotland on the day she was killed to spend time with friends and to remove items from Abboud's home.
The attack at the house was witnessed by neighbour Chloe Forbes Kindlen, who told the court that she went into shock after seeing Abboud plunge the knife into Ms Agnieszka.
In her 999 call, Ms Forbes Kindlen said: "I saw somebody getting stabbed. The guy was stabbing her in the garden."
She added: "She's saying 'ow ow ow'. I just see somebody lying and there's blood. I don't know if she's dead."
The court heard Abboud had then repeatedly stabbed himself to make it look like he was in a struggle and placed the knife under Ms Agnieszka's body so it appeared she had been in possession of the knife.
Abboud will be sentenced at the High Court in Edinburgh on 21 January 2016.
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