Published Friday, 06 December 2013
McNally pleaded guilty to murdering Lauren and trying to murder her sister Brenda - the mother of his two children - in a dramatic, last-minute turn of events in court in October.
The 27-year-old, from Station Road in Toome, had been told at the time that the only sentence for murder was life in prison.
On Friday, Mr Justice Treacy branded the killing "an act of extraordinary wickedness" and ordered that McNally must serve a minimum of 20 years before being eligible for parole.
At the time of the gun attack, McNally's relationship with Brenda O'Neill had already broken up - they had two young children, but Brenda had made it clear it was all over.
McNally went to her home armed with a shotgun and ended up shooting dead her younger sister at point-blank range, before turning the gun on his ex.
What Lauren did was the epitome of bravery. No greater love has anyone than to lay down their life for the ones they love.
John O’Neill, Lauren’s uncle
It had previously emerged in court that his two children - aged just 2 and 10-months-old respectively at the time - had been in the house when the horrific shooting happened.
"Bad daddy," the little girl was said to have shouted, after McNally shot her mother.
Brenda O'Neill survived the shooting, but required emergency surgery and spent over three weeks in hospital - missing her sister's funeral as a result.
Lauren, who had just turned 18, was said to have made the ultimate sacrifice in trying to protect her big sister before losing her own life.
"This case is characterised by features which make it especially serious - the victim was young and completely defenceless with no means of escape," Mr Justice Treacy said.
"He intended to kill both Lauren and Brenda. The murder and attempted murder both took place in full view of his two very young children.
"The cruelty and mercilessness of these actions have left a family physically and mentally broken."
© UTV News