A Perth man who murdered a partygoer with a pair of scissors will spend at least 15 years behind bars.

Ashley James Gunson, 24, fatally stabbed Jamie Devine, 20, in the heart at a 21st birthday party in Atwell in January last year.

He was sentenced in the West Australian Supreme Court on Wednesday to life in prison.

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Gunson was also sentenced to 12 months prison for stabbing Brodie Brouns during the same altercation. That will be served concurrently with the other term.

Justice Ralph Simmonds said Mr Devine had not been involved in the altercation between Gunson and other partygoers before he was stabbed.

“You had no reason to see a threat from him,” Justice Simmonds said.

“You intended to cause a serious injury.”

Justice Simmonds accepted the attack was not premeditated but the result of anger fuelled by alcohol.

He said Gunson’s alcohol consumption that night had been reckless and said he could not be considered a person of prior good character.

Justice Simmonds noted Gunson began drinking when he was 11 years old and was also a drug user.

The court previously heard from Mr Devine’s mother, Pauline, who said in a victim impact statement her heart still ached knowing she would never hug her son again.

“I have no idea how I’m supposed to live the rest of my life without him,” she said.

“There is a huge, empty space in our lives that will never be filled.”

Ms Devine said her son, a young father, had been looking forward to celebrating his own 21st birthday weeks after the party.

Justice Simmonds said Mr Devine’s two-year-old daughter would have to grow up without a dad, and noted Gunson was also a father to a 15-month-old boy.

Gunson’s sentence was backdated to January last year.