Malaysia's prime minister Najib Razak said on Wednesday that "an international team of experts have conclusively confirmed that the aircraft debris found on Reunion Island is indeed MH370".
The barnacle-encrusted wing fragment was sent to France, where experts began examining it on Wednesday. Investigators will analyse the metal with high-powered microscopes to probe what caused the plane to go down.
The Boeing 777 disappeared after veering far off its planned northerly course from Kuala Lumpur in Malaysia to Beijing.
The first ever physical evidence of the aircraft was found on the French territory of Reunion Island, thousands of miles from the site near Australia where the plane is believed to have gone down.
"We now have physical evidence that, as I announced on 24th March last year, flight MH370 tragically ended in the southern Indian Ocean," Mr Najib said in Kuala Lumpur.
"The burden and uncertainty faced by the families during this time has been unspeakable. It is my hope that this confirmation, however tragic and painful, will at least bring certainty to the families and loved ones of the 239 people onboard MH370. They have our deepest sympathy and prayers," he said.
In a statement, Malaysia Airlines said the flaperon, part of the plane's wing, found on Reunion Island on July 29 was confirmed to be of Flight 370 by the French agency that investigates air crashes, known as the BEA, the Malaysian investigation team, a technical representative from PRC and the Australian Transportation Safety Bureau in Toulouse, France.
"Family members of passengers and crew have already been informed and we extend our deepest sympathies to those affected," it said.
The statement said this "is indeed a major breakthrough for us in resolving the disappearance of MH370. We expect and hope that there would be more objects to be found which would be able to help resolve this mystery."
At a press conference in Paris, authorities were much more cautious than the Malaysian prime minister. Deputy French Prosecutor Serge Mackowiak didn't outright confirm that the debris belonged to flight MH370 but said there were strong indications that it was the case.
"The very strong conjectures are to be confirmed by complimentary analysis that will begin tomorrow morning," Mr Mackowiak said. "The experts are conducting their work as fast as they can in order to give complete and reliable information as quickly as possible."
Jacquita Gomes, the wife of crew member Patrick Gomes, said she was informed by Malaysia Airlines about the news half an hour before Mr Najib's announcement.
"Now that they have confirmed it as MH370, I know my husband is no longer of this world but they just can't leave it with this one flaperon. We urge them to continue searching until they find the plane and bring it back," she said.
"We still need to know what happened. They still need to find the plane. They still need to find the black box to get the truth out," she said. It brings some sort of closure but not a complete closure. We don't know what happened and where the plane went down. It's not over yet."
Technical efforts to extrapolate the jet's final hours before it would have run out of fuel gave force to the theory that it went down somewhere in the southern Indian Ocean. No one is certain why the plane deviated so far from its planned route.
Analysts have said a close look at the wing part could indicate what kind of stress the plane was under as it made impact. It won't fully solve the mystery of why the plane disappeared, nor will it help pinpoint where the plane crashed.
A six-week air and sea search covering 4.6 million square kilometres (1.8 million square miles) of the southern Indian Ocean surface early last year failed to find any trace of the jet. The Reunion Island debris would be consistent with the working theory that the jet went down in the Indian Ocean and the debris travelled with the ocean current which moves counter-clockwise.
Malaysian officials, who are leading the investigation into the plane's disappearance, have said the plane's movements were consistent with deliberate actions by someone on the plane, suggesting someone in the cockpit intentionally flew the aircraft off-course.
Since last year, Australian officials who are leading the search effort have operated on the theory that the plane flew on autopilot for hours before running out of fuel and crashing into the ocean. Investigators settled on this scenario after analyzing data exchanged between the plane and a satellite, which showed the plane took a straight path across the ocean.