Serge Mackowiak told a Paris news conference that investigators came to their conclusion for two reasons: Boeing's confirmation that the wing piece discovered is from a Boeing 777, the model of the missing plane; and Malaysia Airlines' information about the specific plane.
"This very strong presumption will have to be confirmed by other analysts who will begin their work tomorrow," he said.
Malaysian Prime Minister Najib Razak was confident enough in the analysis that he held a news conference early on Thursday local time where he announced the wing segment was "indeed from MH370."
In a statement, Malaysia Airlines said the debris was confirmed to be from Flight MH370 by the French agency that investigates air crashes, known as the BEA, the Malaysian investigation team, a technical representative from China 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."
'A needle in a field full of haystacks'
Arthur Rosenberg, a former commercial pilot, noted to CBC News that the Malaysian prime minister sounded more certain than the French prosecutor.
He still expects it is the Malaysian airliner, because only one 777 crashed in that part of the world, and the plane is put together in Spain.
Assuming it is MH370, Rosengberg said analysis of the wing will involve looking at the damage as well as the organisms that have clung to the debris since it first entered the water.
"It's not going to answer that key question that we all want to know: how it happened and why it happened? Maybe with some luck we'll get those black boxes."
Simon Boxall, a tidal drift expert with Southampton University in England, told CBC News that the discovery of the wing piece shows that the original search area was correct. The debris turned up where you would expect it to at the right time.
However, it won't help narrow the search area where the plane's black boxes likely sank.
"They're definitely looking in the right place, but the problem is the right place is huge," he said. "It is looking for a needle in a field full of haystacks."