Dean Lowe is facing life in prison after using a rock and a metal pole to kill Kirby Noden in the bedroom of their basement flat in Marazion, Cornwall, sometime in January 2017.
The 33-year-old who denied harming Ms Noden, 32, claimed she had set him up by spraying her own blood around the one-bed home before leaving him for another man.
Lowe went on trial at Truro Crown Court on April 24 accused of murder and the alternative charge of manslaughter.
On Thursday after deliberating for nine hours and 35 minutes, a jury of six men and six women found him guilty of murder.
Lowe, who was not in court to hear the verdict, earlier described how he and Ms Noden spent Christmas 2016 together "taking drugs and self-harming" and that he last saw her around January 10 - 15.
He claimed she left him for another man and was living in South Africa.
However, the prosecution said Lowe actually beat Ms Noden to death and then disposed of her body and that she must have been dead by January 14 when Lowe attempted to use her bank card to withdraw money from an ATM.
"Having killed her, the defendant moved her body, probably in pieces, and cleaned up the worst of the blood and cutting away the worst of the carpet," said Paul Dunkels QC, for the prosecution.
"For four months, from mid-January to mid-May, he lived on in the flat in the state it was in. Living in the midst of what he had done must have been gruesome."
Mr Dunkels said Ms Noden's blood was "splattered" around the bedroom from the attack upon her, soaked into the mattress where her body had been laying and it was on the weapons he had used to murder her.
He said: "No one other than the defendant knew what had happened to Kirby Noden for five months until May of last year when the defendant began to send text messages to members of his family in Cheshire that there has been a body on the floor of the flat which he had cut up and put into bins and down the toilet."
Jurors were shown images of blood stains discovered in the flat by police on the walls, ceiling and mattress.
They were also shown text messages sent by Lowe.
He told a cousin: "She's dead and has been chopped up and put down the toilet and in the bins down the road.
"Either I'm getting set up or I've murdered Kirby. I had a blackout, hazy memory and woke up with a body on the floor. I am scared so I just got rid.
"I put the body in the bins down the road. I remember the binmen finding all the meat and didn't know what it was. The carpet was lifted because of the body matter.
"It took a week to get rid of the body, it was horrible. (My) head's gone. I know what I saw, it was real, it seems real. Either Kirby dead or set up."
In his evidence, Lowe, of Beacon Road, Marazion, told jurors he had known Ms Noden since they were children because his father and her mother had been friends.
The couple, originally from Winsford in Cheshire, started a relationship aged around 25, later moving to Torquay together before becoming homeless and walking the coast path to Cornwall before they ended up in Penzance.
Summing up the case to the jury, Mrs Justice May said they "stayed in a tent" before moving to the Marazion flat and that Lowe described this as a bad time because they had been "homeless quite a lot, drinking on the streets, taking drugs and trying to forget bad memories".
After taking the verdicts, the judge Mrs Justice May said she wanted time to consider before sentence and asked Anna Vigars QC to provide any relevant details from psychiatric reports done on Lowe.
The case was adjourned to Tuesday for sentence at Exeter Crown Court.