"Overnight into Friday, after accomplishing inspection and customs control, Arctic Sunrise under its own power left [Russia's northern port city of] Murmansk," the group said.
The vessel was seized by Russian authorities following the September arrest of 28 Greenpeace activists and two freelance journalists, dubbed the Arctic 30. The group last year used Arctic Sunrise to gain access to the Prirazlomnaya rig, deployed by Russian energy company Gazprom for work in the country's arctic waters.
The Russian Foreign Ministry said the action "had the appearance of extremist activity." Greenpeace said it was concerned about the potential for an oil spill in the harsh arctic environment.
The ship's captain, Daniel Rizzotti, said in a statement posted on a Twitter site used by the activist group that campaign for the arctic wasn't over.
"We sail home with the voices of 5 million Arctic Defenders in our ears," he said "This is a new beginning."
Greenpeace activists in May staged a similar protest against Gazprom and Norwegian energy company Statoil for their planned operations in the frigid northern climate.