David Payne, 51, from Kilmarnock, killed 42-year-old Alexis Flynn because he thought she was having an affair.
During a 999 call Payne claimed Miss Flynn had attacked him with a knife and he had only stabbed her two or three times. When police arrived, he was smoking a cigarette and drinking a can of beer.
At the High Court in Glasgow, Payne was ordered to serve at least 14-and-a-half years behind bars before he can apply for parole.
At the time of the offence Payne was barred by a court order from approaching Miss Flynn after an alleged assault on her.
Judge Lord Burns told Payne: “You have accepted responsibility not only for the death of your partner Alexis Flynn but also for murdering her.
“It appears that the assault was a sustained one with a knife and she was found with a total of 11 stab wounds on various parts of her body inflicted with a substantial-sized knife.
“The assault must have been prolonged, it is somewhat chilling you were found in the circumstances that you were found, apparently calm, smoking a cigarette, drinking a can of beer.”
The court heard that at about 10:20pm on 10 April this year, Payne phoned 999 and said his partner was dead. When police arrived at the house Miss Flynn was lying on the floor with “obvious stab wounds over her stomach and back”, she was in the foetal position with a large silver kitchen knife in her right hand.
Mr Ewing added: “Payne was sitting on a couch next to the deceased, he was smoking a cigarette and drinking from a can of beer.” Officers took the knife out of Miss Flynn’s hand and started CPR but saw she had been dead for some time.
Payne told officers “she stabbed herself”. During his police interview the following day Payne, who has previous convictions for domestic assault and breach of the peace on his ex wife, claimed Miss Flynn was attacked by a neighbour.
Mr Ewing said a post mortem revealed Miss Flynn died of a stab wound to the leg that damaged large blood vessels that “would have caused rapid and profuse blood loss and death”.
The court heard injuries to her lungs, stomach and kidney were “potentially survivable” but the stab wound on the left thigh was “catastrophic”.