Rodney Dempsey, 53, last month pleaded guilty to murdering 27-year-old Jenoa Sutton, whose body was found in the bathroom of her Lithgow home, west of Sydney, on March 8, 2012.
The couple parented two young children together during their on-and-off relationship before officially separating in 2011.
Justice Peter Hamill said their relationship had been fraught but never physically violent until the day Dempsey killed Ms Sutton.
"Mr Dempsey was possessive, regularly intoxicated and often verbally abusive to Ms Sutton but until the day of the murder he had not been physically abusive," he told the NSW Supreme Court on Friday.
While Justice Hamill did not believe the murder was planned, he was satisfied Dempsey had formed an intention to kill her and was motivated by "his love of his children and fear of losing them".
Justice Hamill called it an "extreme case of domestic violence" before sentencing Dempsey to 19 years and nine months in prison with a non-parole period of 14 years and six months.
Dempsey used a rectangular object, possibly a piece of wood, to strike her and caused a "ferocious" blow to the back of a head with an object that may have been a hammer.
The hit caused a depressed skull fracture and embedded 10 skull fragments into her brain.
Dempsey showed no emotion as the judge handed down the sentence, while Ms Sutton's family cried.
He will be eligible for parole in 2034.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
9°C