The British backpacker was strangled to death on the eve of her 22nd birthday by her Tinder date in his downtown Auckland apartment on December 1 last year.
He then went about trying to cover it up and dumped her body in the Waitākere Ranges.
Millane's parents, seated in the first row of the public gallery, broke down in tears and embraced each other as they heard the word "guilty" from the jury foreperson.
David and Gillian Millane spoke to dozens of journalists from around the world after the verdict.
David said their lives had been ripped apart.
His only daughter, he continued, "did not deserve to be murdered in such a barbaric way in her OE year".
Millane's parents thanked several people, including Auckland Police, specifically Detective Inspector Scott Beard, Detective Sergeant Greg Brand and Detective Toni Jordan.
"We would like to thank the Crown prosecution team: Brian [Dickey], Robin [McCoubrey], and Litia [Tuiburelevu]. They never flinched away from the more intimate details of the case and were compassionate and thoughtful where the family matters arose.
"The press contingent ... you attended court every day with my wife and I and reported truthfully, respectfully all the events as they unfolded."
The Millanes also thanked the people of New Zealand.
"They've opened their hearts to Grace and her family, I cannot express our gratitude enough for all the offers of gifts and kindness that we've received over the last year."
The Millanes will now return to England and "try pick up the pieces of ours lives" and live day-to-day without their beloved daughter.
Millane's parents left the court on the 12th day of the trial as they had entered on the 1st - holding hands and in tears.
The jury's decision was unanimous. But even some of the members of the jury broke down and sobbed as they left the courtroom for the final time.
Different narratives
After hearing from nearly 39 witnesses over nearly three weeks they were presented with two different narratives about what happened to Millane on that fateful night.
Dickey and his team said it was murder.
They used some of the six terabytes of CCTV footage collected by police to track the killer's movements, his internet search history, expert witness, and those who knew the murderer's inclination to dominate women.
He strangled Millane to death in his CityLife hotel room and then took "trophy" photos of her body, Dickey told them.
The killer "eroticised the death of British backpacker Grace Millane" because of his "morbid sexual interest".
The defence, however, used expert evidence and those who knew Millane to say it was an accidental death during erotic asphyxiation.
The killer had "freaked out", his chief of defence Ian Brookie said, before then lying to police and trying cover it up.
The 27-year-old murderer, who had shed tears throughout the trial, appeared anxious as he walked into the dock to hear his fate this afternoon.
But this time the man, who cannot be named for legal reasons, held back his tears.
He gulped and took a big breath before hearing the foreperson deliver justice for the Millane family.
"This jury having found you guilty of the murder of Grace Emmie Rose Millane, you are convicted," Justice Simon Moore told him.
Leaving the dock with his head down, the killer will return to court on February 21 at 9am to be sentenced.
The murderer's stepbrother told the Herald after the verdict he shed tears but was "so glad for Grace's family".
"It doesn't make anything better, but [it's] good to know the jury and New Zealand justice system made the right call."
Justice Moore told the jury "it is never easy to judge a fellow man".
"It is evident each of you has thought very hard and very careful," he said. "This has been a particularly difficult trial."
The judge discharged them all from sitting on a jury for the next seven years.
During their deliberation the jury knocked on the courtroom door about 4.45pm to ask a question.
They asked: "Does 'when he applied pressure' [to Millane's neck] refer to when he started to apply pressure at the beginning or can it refer to any time when he applied pressure?"
Justice Moore answered: "It is not limited to the beginning. It can be at any time during the application of force leading to death."
It may have been a hint as to which way they were leaning because just an hour later they returned with their guilty verdict.
Beard said because of the ongoing court process police were unable to comment about the case.
