Marion Graham, 54, from Newry, and her 53-year-old friend Cathy Dinsmore, from Warrenpoint, were killed in August 2011 while on holiday in the country.
Their bodies were found buried in shallow graves in woods 75 miles outside the popular resort of Kusadasi where they were staying.
Marion had been stabbed 17 times, while Cathy suffered 37 stab wounds.
On Wednesday, Recep Cetin, 24, was found guilty of the double murder at a court in Izmir.
He is expected to serve the rest of his life behind bars for the killings, but could apply for parole in 30 years time.
He had been dating Ms Graham's 15-year-old daughter Shannon at the time of the murders.
Cetin's father Eyup, a taxi driver, who was also accused of the murders, was cleared and was released from custody.
The Turkish waiter had admitted stabbing the women but maintained his father, who consistently protested his innocence, was not involved.
As he was led away from the dock with his hands cuffed after sentencing, he turned around and looked at Shannon and then was taken away to jail.
We got a verdict and the closure. That's what we came here for and we have got it.
Cathy's brother, George Dinsmore
During a previous court appearance last month, Cetin had expressed regret for the killings, which he claimed were carried out because he was in love.
"I did it so I would not lose my girlfriend," he said.
Relatives of both women, including Shannon, flew out to Turkey for the court hearing which had been adjourned last month.
Outside court, Shannon told UTV's Sharon O'Neill the killer had torn her family apart. She said she was satisfied after the verdict.
George Dinsmore, Cathy's brother, said they had finally got the justice they had been hoping for.
"We are very, very relieved," he said.
Before travelling to Turkey, George told UTV he has been consumed by what ifs since the double murder.
For somebody so quiet, who never harmed anyone, to get killed so brutally... It just doesn't make sense.
"A couple of days beforehand she couldn't find her passport to go, and she had to get a taxi to Dublin to get a new passport and it has always been in my mind that if she hadn't got the passport she wouldn't have been there," he said.
He added: "It's something (Cetin) had been getting ready to do, it wasn't something that happened in the spur of the moment."
"It's pure evil. I can't understand how somebody can do that."
Cetin initially tried to cover up the brutal double murder, claiming the women had been kidnapped.
But he became a suspect when their bloodstained clothes were found in a bin near his family home.
After his arrest Cetin admitted to stabbing the women in self-defence but denied murder.
For two years he tried to stall the legal process and falsely claimed to be aged 17 in an apparent attempt to be tried in the juvenile courts where sentences are lighter.
He was ordered to undergo bone marrow tests which determined he was in his 20s.
Last month the judges also dismissed claims he was insane.