The decision means that Mr Pora is a free man. His parole conditions immediately fall away.
The news was broken to Mr Pora by his support team, which includes private investigator Tim McKinnel and lawyers Jonathan Krebs and Ingrid Squire, about an hour before the decision was announced by the Privy Council last night.
He was surrounded by about 30 supporters including his daughter Channelle Bennett, grandson Benson, 5, and Pastor Billy Retimana and his wife Winnie, whose home Mr Pora has been living at since being released on parole.
"He has been subject to some extraordinarily strict parole conditions, they've gradually relaxed as he's become more comfortable in the community."
Mr Pora had a job and a network of friends, Mr Krebs said.
"He's in a position now where he's working, he's well adjusted in the community, he's done a little bit of study, he's built up a network of friends."
Now that he was a free man that life would continue, Mr Krebs said.
Delivering the decision, Lord Kerr said evidence from two medical experts that Mr Pora suffered from a form of fetal alcohol spectrum disorder - and in their opinion that could explain why he made what is now believed to be false confessions - was a big factor in the outcome.
The condition meant Mr Pora would have had a very low IQ - that of a child's - when he was interviewed by police, at age 17.
"The board concluded that the opinions of these experts called seriously into question whether the confessions could indeed be regarded as reliable," Lord Kerr said.
"And since they were the central and critical evidence at both his trials, it was concluded that there was a risk of miscarriage of justice if Mr Pora's convictions were to be allowed to stand.
"The board decided, therefore, that those convictions had to be quashed and that Mr Pora's appeal be allowed."
The board will now give an opportunity for submissions to be made - over the next four weeks - on whether another retrial should take place.
Private investigator Tim McKinnel told Radio New Zealand that a retrial for Rewa was a possible outcome from the Privy Council's decision.
He said the team behind Mr Pora's appeal weren't concerned about the prospect of him facing a retrial, but saw it as another opportunity to put forward the facts of the client's wrongful conviction. But Mr McKinnel held a different personal view.
"My personal view is that I don't think there ought to be [another retrial]."
He hinted that there was more to be told about Mr Pora's case that would come out in due time.
"There's a lot of things we want to say in time about this case... but we really need to be so careful at the moment as we take the next step."
Mr McKinnel said it was an emotional time for Mr Pora after such a long time in prison. "Teina is overjoyed and overwhelmed."
The decision was reached by a panel of the judicial committee of the Privy Council made up of the New Zealand Chief Justice, Dame Sian Elias, and four Law Lords, including Lord Kerr.
Lord Kerr said written submissions on whether a retrial should be held would need to be filed within four weeks. "Those convictions had to be quashed and that Mr Pora's appeal be allowed," he said.
Reaction to the Privy Council decision
Mr Krebs told the gathering for Mr Pora that they were delighted that the Privy Council did not automatically order a re-trial and said it was a 99.9 per cent result, to cheering from supporters. "He's the man, he's the innocent man. It's your night Teina."
Mr Pora's daughter hugged her father and said of the decision: "That's so good to hear."
Mr Krebs said last night Mr Pora was initially speechless when the decision was announced.
"He's probably the happiest man in the country tonight. He has spent the last 22 years in some Sort of Administrative custody. What will happen tomorrow? He will not be subject to parole conditions anymore. He's essentially altogether free. Tomorrow he'll still be smiling - there's no doubt about that."
He said Mr Pora thanked everyone who had supported him in his fight to clear his name. He also wanted to acknowledge the "incredible" and "magnificent" support of the Burdett family.
Mr Krebs said the issue of compensation for Mr Pora would be considered later - as would any questions around the police case and an apology.
"We're not done yet," Mr Krebs said.
Case for compensation
Police Assistant Commissioner Malcolm Burgess said police would take time to "fully consider the judgment and expect to be consulted by Crown Law regarding any Crown submissions on re-trial".
He cited a comment from the Privy Council which relation to Mr Pora's confession: "In the present case it is clear that none of the police officers exerted pressure on Pora. Indeed, they were, if anything, fastidiously correct in their treatment of him."
In November, Solicitor-General Michael Heron, QC, told the Herald that even if the Privy Council recommended a retrial, one might not be held.
"Whatever the court said in their decision would be very strongly taken into consideration in whether or not there would be a retrial," a spokeswoman said at the time.
Mr Pora was 17 and the father of a toddler when charged with the crimes and imprisoned on remand. He is now a 39-year-old grandfather. He may have a strong case for compensation.
Mr McKinnel said compensation for Mr Pora's 22 years in custody could be looked at at a later date.
The Privy Council wouldn't accept evidence put forward by Mr Pora's legal team regarding serial rapist Malcolm Rewa.
However, Mr Krebs said this didn't weaken their position, "not a jot", if a retrial was ordered for Mr Pora.
He said providing evidence for an appellant court, especially the Privy Council, was more difficult than calling witnesses in a regular trial.
If a retrial was not ordered the issue of compensation would then be looked at, Mr Krebs said.
In 2001, the Government awarded David Dougherty $868,728 compensation after he spent more than three years in prison for an abduction and rape of an 11-year old girl that he did not commit. The figure was recommended by Stuart Grieve, QC, who was commissioned by the Government to assess Dougherty's eligibility for compensation.
Ms Burdett's brother Jim said he was pleased Mr Pora had been vindicated. "To me the evidence seems pretty conclusive. I'm happy insofar as this poor guy has spent 21 years in jail for something he didn't do and having a sense that this is going some way towards justice. I have, for literally years now, believed that Teina Pora did not kill my sister."
Mr Burdett told Radio New Zealand a meeting with Mr Pora was a possibility, but the decision would be left to Mr Pora.
"It's Teina's call really, it's up to him."
Mr Burdett said while he hasn't met Mr Pora he has communicated with him through private investigator Tim McKinnel.
He said he felt sad for what Mr Pora had been through.
"My feeling is that it's a sad state of affairs for someone to spend his whole adult life in jail for something he didn't do."
He said he had moved on and dealt with his grief about his sister's murder some years ago.
Miscarriage of justice
Labour's justice Spokesperson Jacinda Ardern said the case should have been closed years ago.
"Teina Pora has spent more than 20 years in prison, despite overwhelming public evidence that a miscarriage of justice occurred.
"The decision of the Privy Council to uphold his appeal has come with a hefty price tag not only for all the families involved in this case, but also the justice system.
She said Labour had been calling for a Criminal Cases Review Commission - an independent body to deal with claims of wrongful conviction and miscarriage of justice - for several years.
"In countries such as England, Scotland, and Norway commissions act as a safety valve for the justice system, ensuring miscarriages of justice are properly investigated and remedied.
"In New Zealand it would essentially replace the Royal prerogative of mercy process, which is a lengthy and potentially conflicted procedure, leaving the decision to the ministry responsible for administering the justice system.
"Had a Commission been established here it would have provided a far more streamlined process for Teina Pora's case.
"Instead our justice system failed Teina Pora. It's our job to make sure that never happens again."
Dean of the University of Canterbury's School of Law, Associate Professor Chris Gallavin agreed with Ms Ardern about the comission.
"If for no other reason the Government would likely save money through the establishment of such a panel as these high-profile defeats are extremely expensive and ultimately damaging to the reputation of our justice system."
Former Justice Minister Judith Collins in 2013 rejected calls for the establishment of a an independent body to be set up to remedy miscarriages of justice following the Privy Council's decision to throw out Mark Lundy's double murder convictions.
A Criminal Cases Review Commission was established in the UK in 1997 and has since seen 18,500 applications for review filed.
"The (David) Bain case, the Lundy case, now Teina Pora and not to mention the serious concerns that still hang over the Peter Ellis investigation, trial and conviction and also the Scott Watson case illustrate that problems do occur within the system for which the process of appeal is not entirely equipped to deal with," Dr Gallavin said.
"In terms of Teina Pora, the Privy Council has taken the remarkable step of seeking submissions on the issue of whether there ought to be a third retrial. In my opinion there most certainly should not be and the quashing of the conviction by the Privy Council should be deemed final."
Justice Minister Amy Adams wouldn't be available for an interview today, but provided a statement saying the system for appeal within the New Zealand justice system was highly regarded and robust.
"From time to time the issue of setting up a Criminal Cases Review Commission has been raised with successive Governments but none have progressed the idea.
"Establishing an independent body to deal with miscarriages of justice applications would essentially just replicate the process already available through the Royal Prerogative of Mercy.
"I consider it appropriate that determinations of guilt and reviews of those determinations remain principally with the judiciary."
Serial rapist
Mr Pora was first convicted in 1994 of Ms Burdett's rape and murder on the basis of his confessions.
In 1996, DNA from semen at the scene linked the attack to Malcolm Rewa, a serial rapist with a modus operandi of offending alone. Rewa was eventually convicted of the rape of 27 women, including Ms Burdett, but two juries could not reach a verdict regarding murder.
Mr Pora was again convicted of rape and murder at a retrial in 2000 and his appeal to the Court of Appeal was dismissed.
The Privy Council spent two days last November hearing fresh evidence. Mr Pora's team argued that the new evidence - an expert opinion on false confessions and a recent assessment that he is affected by fetal alcohol spectrum disorder - supported the claim that his confessions could not be relied on.
The other ground was that because of an error by his trial lawyer, the significance of Rewa's erectile dysfunction was never put to a jury.
The case has become one of the country's most controversial and raises questions about the disclosure of information to defence lawyers, the use of paid witnesses and the adequacy of New Zealand's system of dealing with miscarriages of justice.
Battered to death
Ms Burdett was a 39-year-old accounts clerk and an avid ten pin bowler who lived alone. She returned late from club night at the Manukau Superstrike on Monday, March 23, 1992, and was raped, then battered to death. Her killer crossed her legs, which were positioned off the bed. Lying on the bed beside her was the softball bat she kept for protection.
In the months after the attack, Mr Pora was among hundreds of men who gave DNA samples that cleared them of having left the semen at the scene.
On March 18, 1993, nearly a year after the murder, Mr Pora was arrested on warrants for failing to attend court on car theft charges. He was 17, the son of a teenage mother who died when he was aged 4 and a father who was never around. Mr Pora was a father himself: he had a baby daughter.
He also was in a bitter dispute with senior Mongrel Mob members, having pinched back a car they had taken from him. He knew the gang were after him, and he was in trouble with the police too.
His defence team said Mr Pora sought to ingratiate himself with the police by implying he knew who was responsible for killing Ms Burdett. He was told a $20,000 reward was available. During two days of questioning by police without a lawyer he told stilted, vague, contradictory stories claiming Mobsters were responsible. In total he named five men, all cleared by DNA.
Mr Pora may have been foolish but the Privy Council ruled that the evidence does not make him a murderer.
A brutal murder, a fight for freedom: Teina Pora timeline
1992, March 23: Susan Burdett raped and murdered in her home in south Auckland.
1993, March 23: Teina Pora charged with burglary, sexual violation and murder.
1994, June: Pora convicted as a party to the rape and murder on the basis of confessions he made. Sentenced to life in prison.
1996, May: Rewa arrested after attacking a young woman in the inner Auckland suburb of Remuera, DNA from Rewa's father found to match semen from Burdett crimescene.
1998: Rewa eventually convicted of the rape of 27 women, including Ms Burdett but two juries fail to reach a verdict on murder.
1998, May 30: In 1998 Rewa was convicted on multiple sex charges dating back to 1987 and sentenced to preventive detention with a minimum non-parole period of 22 years. He was convicted of the rape of Ms Burdett the following year.
1999: Court of Appeal quashed Pora's convictions as a result of the DNA evidence implicating Rewa and evidence that Rewa acted alone.
2000, June: Pora was again convicted at his retrial, based on his confessions and witnesses, some of whom it later emerged were paid. His appeal to the Court of Appeal was dismissed.
2009, September: Private investigator and former police detective Tim McKinnel visits Pora in prison and is given permission to make inquires on Pora's behalf.
2011, September: Pora team file notice of application for the Royal Prerogative of Mercy but two years later are granted an appeal to the Privy Council.
2012, May: Police's criminal profiling expert goes public in Herald with view Pora not involved; Pora's team sue police claiming it is unlawfully withholding evidence, Ms Burdett's brother says Pora is innocent.
2013, February: It is revealed police paid some prosecution witnesses.
2013, August: The Police Association call for an independent inquiry into Pora's convictions.
2014, April: Pora granted parole at his 13th appearance before the board and after spending 21 years in jail.