Haiti has been rattled by at least 50 tremors since the original quake.
The survivor, a man in his early 30s, was pulled from the ruins covered in dust.
"He was buried in the rubble for 12 days. The man had a broken leg and severe dehydration," a statement from the US military said.
The Associated Press named the man as Rico Dibrivell and said he was discovered initially by a group of Haitians who pulled him from the rubble of a shop that had been repeatedly looted.
Although he had apparently been trapped by an aftershock rather than the initial earthquake, the man is the longest survivor so far under the rubble.
A rescue team has also been digging into the rubble of a university, after a man said he had managed to phone his cousin who said she was trapped in a basement, along with several other people.
Some bodies have already been pulled out but as yet the woman has not been found.
On Saturday, Haiti's government declared the search and rescue phase over.
It is estimated more than 130 people have been pulled alive by rescue teams in the Haitian capital since the quake.
However, many more have been rescued by ordinary Haitians, often with their bare hands.
Aid call
Earlier, Haitian President Rene Preval made an urgent appeal for more tents to house up to a million people left homeless by the tremor.
Rico Dibrivell was rescued from the rubble after being trapped for 12 days
Mr Preval said 200,000 tents were needed before the expected start of the rainy season in May.
His call came as donor nations and organisations met in Montreal, Canada, to assess the aid effort.
In an interview with the BBC, the president's wife, Elisabeth Preval, appealed for patience as criticism grew about the government's response to the disaster.
"The president is working 24 hours a day, continuing to assess the damage, trying to direct the aid relief where the Haitian people need it" she said.
She added that the administration had been overwhelmed by the disaster, but that ministers had managed to get on to the streets on the day of the earthquake to assess the damage.
The president, who lost his house in the quake, is planning to move into a tent on the lawn of the destroyed National Palace in the centre of the capital.
The Haitian government wants to relocate some 400,000 people, currently in makeshift camps across the capital, to temporary tent villages outside the city.
But aid workers warned that if the camps were too big they could pose security problems, including robberies, rapes and gang activities.
Meanwhile, US Secretary of State Hillary Clinton said she "resented" criticism of American assistance to Haiti.
She pinpointed some media outlets which had "either misunderstood or deliberately misconstrued what was a civilian and military response".
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