Anthony Clarke, 27, had bundled his Polish-born ex-girlfriend Monika Szmecht, 21, into a van and held her hostage for more than four hours, jurors at Liverpool Crown Court were told.
He then drove her to an isolated country lane near the village of Rainford, St Helens, where she was repeatedly stabbed and set on fire, the court heard. When she did not die Clarke continued the stabbing frenzy before leaving her for dead.
But the 21-year-old survived long enough to crawl 150 yards to a house and, moments before she died, named Clarke as her attacker when paramedics asked who was responsible.
Clarke, a former soldier, of Halsey Crescent, West Derby, had denied murder but the 11 jurors returned a unanimous guilty verdict after five hours of deliberations.
Clarke was originally charged with murder alongside his uncle, David Clarke, 46, of Walton Village, Liverpool, and best friend Philip Savin, 29, of Chester Avenue, Bootle, Merseyside.
But on the day the trial was due to begin, both Savin and David Clarke agreed to plead guilty to lesser charges and give evidence for the prosecution.
Savin described how Anthony Clarke became increasingly angry that Ms Szmecht, who worked at the Bar Italia restaurant in Liverpool city centre, was receiving text messages from a man. It was later established the man was not her new lover but her landlord.
David Clarke has pleaded guilty to assisting an offender and Savin has pleaded guilty to kidnap, making threats and assisting an offender. Both will be sentenced alongside Clarke on Friday.
Merseyside Police put armed officers around the court building for the verdict as the three men are thought to have links with Liverpool's criminal underworld. The court has also been told that when he heard his uncle would give evidence against him, Anthony Clarke threatened to have David Clarke's wife, his own aunt, shot.