Lorraine Cox, 32, was killed in Exeter on 1 September.
Azam Mangori, 24, of Dartmouth Road, Stoke-on-Trent was found guilty of murder, having previously admitted preventing a lawful burial.
He left Ms Cox’s body for a week in his flat before he “panicked” and dismembered her, jurors at Exeter Crown Court heard.
After the trial police said Mangori had committed a “deeply disturbing” and “horrendous” crime.
Mangori followed Ms Cox through the streets and persuaded her to go to his flat above a kebab shop.
Parts of her body were later found in an alley next to the flat and in woodland at Newton St Cyres, about six miles (9km) away.
Mangori, an Iraqi Kurd who was denied asylum in December 2018, told the court he had panicked because he feared being deported.
Mangori said Ms Cox drank spirits and smoked a mystery drug in his room before losing consciousness and dying.
He said he had dismembered her body because he did not know how to get rid of it after it started to decompose.
But prosecutor Simon Laws QC called Mangori a “fluent and determined liar” and said he had smothered her with a T-shirt.
The court heard after Ms Cox was killed, Mangori used a SIM card from her phone to send messages to her family, partner and friends in an attempt to show she was still alive.
He also looked at amputation videos in the days before her disappearance, jurors were told.
Mangori was caught on camera in shops buying supplies to help him dispose of her body, including bin bags, tape, a suitcase and an air purifier to hide the smell.
He also purchased items, including a trowel, after viewing a website entitled: “How to dig a grave by hand.”
Mangori described the days following her death as “a living hell”.
Judge Justice Garnham said Mangori, who was remanded in custody, would be sentenced for both offences on 7 April.