The university graduate would never leave the room alive - her body later found dumped in a shallow grave in the Waitākere Ranges.
After hearing from nearly 40 witnesses during the highly charged and emotional trial, the jury's decision was unanimous.
Millane's mum Gillian at last month's sentencing said that her kind and intelligent daughter's dream to travel the world had turned into a nightmare that ripped the family apart.
"She died terrified and alone in a room with you ... all her dreams and aspirations taken," Gillian Millane said in a victim impact statement.
Justice Simon Moore said this was not a case where the strangulation was driven by rage or was premeditated.
But Millane was vulnerable and appeared to be restrained, while the 28-year-old killer's actions in photographing her naked body after the murder were "depraved".
"You were in a position of total physical dominance," the judge told the killer last month.
"You were a stranger, she trusted you."
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