Construction of the controversial Dakota Access Pipeline has been halted, with a federal agency denying its backers access to land belonging to the Standing Rock Sioux tribe.
The Army Corps of Engineers told protesters gathered at the site the current planned route for the US$3.7 billion pipeline won't go ahead.
"Today the Army Corp of Engineers announced its decision not to grant the easement to the Dakota Access Pipeline crossing the Missouri immediately above the Standing Rock Sioux Reservation, and to study alternate routes," a statement from the National Congress of American Indians said.
"From the start, the Standing Rock Sioux Tribe has asked for a full analysis to consider threats to the water and environment, and also the social and cultural impacts. Peace, prayer, and the water protectors have led to the right outcome."
"The Standing Rock Sioux Tribe and all of Indian Country will be forever grateful to the Obama administration for this historic decision," Standing Rock tribal chairman Dave Archambault said in a statement.
President-elect Donald Trump has vowed to let the pipeline go ahead. Protesters had previously been given until Monday to leave.
"Individuals found on Army land north of the river after December 5 would be considered trespassing and could be prosecuted," the US Army warned on November 27.
They'd also been warned to leave before winter came, bringing with it snow.
Thousands of protesters have been camped at Standing Rock in recent weeks, regularly getting into violent confrontations with police. Dozens have been hospitalised in the clashes.
The Standing Rock tribe say the pipeline will put sacred sites at risk and threatens to pollute the reservation's land and water supplies.