Hussain Haron, of London Road in Mitcham, has been convicted with the murder of Felecia Cadore.
Police were called to a report of an altercation in Grenaby Avenue, Croydon, on June 9, 2023.
Felecia, aged 29, was found with stab wounds and was taken to hospital in a critical condition.
She then died from her injuries on June 14 that year.
Snaresbrook Crown Court heard that the now 24-year-old climbed through his ex-girlfriend’s window while searching for Felecia.
After an argument between the two, Haron grabbed a knife and violently stabbed her.
He was arrested later that afternoon and was found in possession of the knife he used to attack Felecia.
Despite claiming he was acting in self-defence, Haron was found guilty of murder by the jury.
He was found guilty of murder today (January 29) after a six-day trial.
Haron is due to be sentenced at the same court on Friday (January 31).
Detective Chief Inspector Craig Magee, from Specialist Crime, said: “Today, justice has been served following the conviction of Hussain Haron for the murder of Felecia Cadore in June 2023. It is an example of the devastating impact violence against women and girls can have.
“The verdict is a result of officers working meticulously and tirelessly to secure evidence. It is also testament to the courage of the witnesses who helped establish the facts, and bravely stood in the court room to give their evidence.
“It has been 18 months since Felecia was killed. I hope that today’s verdict provides her family with some comfort and allows them to begin to process the effect this brutal crime has had. We will continue to support the family of Felecia following this horrific attack.”