Lance Corporal Trimaan "Harry" Dhillon, 26, was accused of breaking into Alice Ruggles' flat and slitting her throat from ear to ear.
Dhillon, who was described in a court as an obsessive, controlling and manipulative person, had denied murdering Ruggles in October last year.
But a jury at Newcastle Crown Court today found him guilty of murder and Judge Paul Sloan sentenced him to a minimum of 22 years behind bars before being considered for parole.
Edinburgh-based Dhillon was found guilty of using his skills as a signaller with 2 Scots, the Royal Regiment of Scotland, to hack his 24-year-old victim's emails, phone messages and social media.
She was found dead in a pool of blood by her flatmate Maxine just days after she had told a police officer she did not want Dhillon to be arrested for harassment.
He allegedly left her flowers and chocolates and then walked away.
Dhillon was ordered by his commanding officer to stay away from his ex-girlfriend but he posted her a parcel containing photos and a letter.
According to the prosecution, Dhillon drove to Ruggles' home on October 10 last year and waited for her after he broke in through her bedroom window and took a knife from the kitchen.
His victim also suffered a wound to the nose and her hand, along with chest injuries.
Dhillon had claimed she died as a result of an accident when she leapt at him with a carving knife.
He told the jury they had been struggling, that he had tried to disarm her and she cut herself when he blocked a lunge, and the knife stuck in her neck when she fell to the floor.
The jury played a frantic 999 call by Miss Ruggle's friend Maxine McGill in which she described finding the 24- year-old "covered in blood" and named Dhillon as the killer, calling him an "absolute psychopath".
The jury were told that Dhillon soon set about alienating her from her friends, knocked her self-confidence and demanded her constant attention.
His previous partner suffered similarly and her ordeal only ended after she took out a restraining order.
After the verdict, Ruggles' family released a statement through the Suzy Lamplugh Trust, which helps people avoid becoming victims of violence.
Her mother Sue said: "I just keep thinking I can't believe we didn't identify the signs of stalking but you just don't know when it's going on".
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