Andrea Lewis, 51, was found dead at a home in Fairyland Road, Tonna, Neath, on 30 January 2016, with 43 injuries including to her skull and torso.
Rhys Hobbs, 46, of Tonna, pleaded guilty to manslaughter in July and was sentenced at Swansea Crown Court.
On Tuesday, the Court of Appeal upped his sentence to 12-and-a-half years.
A statement from the Attorney General said the case was returned to the courts by the Solicitor General, Robert Buckland QC MP, under the Unduly Lenient Sentence scheme.
Speaking after the hearing, he said: "Hobbs has a history of violent abuse and has shown very little remorse or regret concerning the incident.
"It's important we send a message that violence in a domestic setting is completely unacceptable and I'm pleased the court has agreed Hobbs should spend longer in jail for his crimes."
During the original sentencing, Swansea Crown Court heard Ms Lewis had been stamped on following a drunken row.
In the weeks running up to her death, she was covered in bruises and had a black eye - but told friends she had fallen.
After Hobbs attacked her in his home, Ms Lewis was dragged outside while half-dressed. She was found dead the next day.
A man who was jailed for killing his ex-girlfriend in a "violent and protracted" attack has had his eight-year sentence increased.