Woodke's release was announced days after US Secretary of State Antony Blinken travelled to Niger for an official visit, becoming the first top US diplomat to visit the country.
"I'm gratified & relieved to see the release of US hostage Jeff Woodke after over 6 years in captivity," US national security adviser Jake Sullivan said on Twitter.
"The US thanks Niger for its help in bringing him home to all who miss & love him."
A senior administration official praised efforts of Niger in helping secure the release of Woodke but declined to say where he was exactly on Monday.
The official, who spoke to reporters by phone and on the condition of anonymity, added that Woodke's family had been notified.
His wife Els said she had not yet heard from him but was told that he was in good condition, a statement on a website calling for his freedom said.
"She has expressed her profound thanks to the many people in governments and others around the world who have worked so hard to see this result. She praises God for answering the prayers of Christians everywhere who have prayed for this outcome," the statement said.
There were no direct negotiations with the militant organisation that held Woodke, and no ransom or so-called quid pro quo was part of his release, the senior US official said.
It was not entirely clear where Woodke was held during his captivity, the official said, but he was known to have been in multiple locations and multiple countries.
The official declined to say which group held him but described it as a "captive network that operates across parts of Niger, Mali and the Burkina Faso area".
Woodke was released outside of Niger.
The New York Times first reported his release.
The official also said Niger was part of the effort that helped free a second US citizen held by the same network, although he did not name that citizen or provide details around their release.
Officials in Niger on Monday also announced that a French journalist had been released in the country.
The reporter Olivier Dubois, who was kidnapped by Islamist militants in Mali in 2021, arrived in the capital of Niger Niamey on Monday after his release, according to the Nigeriean Interior Ministry.
French President Emmanuel Macron wrote "Olivier Dubois is free," on Twitter on Monday.
He called the news an enormous relief for France, journalists and Dubois' relatives, expressing gratitude to Niger for his liberation.
Two members of the Red Cross were also released, the International Committee of the Red Cross (ICRC) said.
They had been abducted in northern Mali on March 4 and were freed on Sunday but the ICRC did not provide further details.
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