Joe Storey, 27, had denied murdering Kerri McAuley, 32, who was found dead at Southalls Way, Norwich, on 8 January, but admitted manslaughter.
Storey was high on cocaine when he punched mother-of-two Ms McAuley after a row about an ex-girlfriend.
The jury at Norwich Crown Court took less than an hour to find Storey guilty. He will be sentenced on Friday.
The court had heard friends describe a history of domestic violence which left Ms McAuley "disfigured" and fearing for her life.
In her texts Ms McAuley described Mr Storey's behaviour as "not normal". She wrote: "you are not ready to care for anyone but yourself".
"You were trying to kill me, you were suffocating me until I nearly passed out", adding that if he stays away "hopefully you won't go to prison for beating me to a pulp".
Later Mr Storey and Ms McAuley agreed to meet up again.
Pathologist Dr Benjamin Swift said in the fatal attack Ms McAuley sustained multiple facial lacerations and one of her ears was torn.
Dr Swift said some of the injuries were caused by "blunt force impact".
Storey, of Murrells Court, Norwich, had admitted the pair had a turbulent relationship.
He said he was staying at Ms McAuley's home when she confronted him about his ex-girlfriend who she thought was back in contact with him.
Storey said he struck her five or six times and had a phone in his hand at the time but insisted he had "not to hit her with it".
Prosecutor Simon Spence said Storey behaved like an animal and if "he'd had a scrap of humanity" Storey would have called an ambulance after the attack instead of leaving Ms McAuley to die in the flat.

The 23-year-old, whose brother Sam has returned to the Rabbitohs after a spell in rugby union, said in May that he was keen to play in the NFL.
Jarryd Hayne, another National Rugby League player, left Parramatta Eels to join the San Francisco 49ers this year.
It is understood the Giants hold weekly trials, and that Burgess was one of many to take part on Thursday.
Burgess, born in Dewsbury, West Yorkshire, began his career at Super League side Bradford Bulls, but only spent two seasons there before moving to NRL club Rabbitohs where he joined his brother Sam and twin George.
The England international was part of the Rabbitohs side that beat St Helens 39-0 to win the 2015 World Club Challenge.
A man has been found guilty of murdering his "on-off partner" by bludgeoning her to death.
[NEXT_CONCEPT]
South Sydney Rabbitohs prop Tom Burgess has had a trial with the New York Giants American football team.