Paul Watson of the Sea Shepherd Conservation Society left a Frankfurt jail on Monday after a court ordered him freed on bail pending a decision on whether he will be extradited to Costa Rica.
Watson is wanted for allegedly endangering a Costa Rican fishing boat while filming a documentary in 2002.
The Toronto-born activist said he was relieved to be free, a week after his detention at Frankfurt Airport.
"I didn't expect something that happened 10 years ago to sneak up on me in Germany," Watson told reporters.
Last Friday, a Frankfurt court ruled that Watson could be freed on $320,000 bail.
Sea Shepherd says the money was put up by a donor and Watson must remain in Germany while the extradition case against him is underway.
"While we have won a victory with the decision to allow Captain Paul Watson out on bail, the battle to save his life must now intensify," Sea Shepherd said in a statement posted on their website.
Watson also issued a statement from his cell last week saying his group has "made some powerful enemies" in its efforts to defend the lives of whales, sharks, seals and other sea life.
"Therefore the question must be asked why Germany is now taking into account accusations made by illegal poachers,'' he said.
Sea Shepherd continues to maintain that Watson's arrest was politically motivated and is calling on its supporters to come together in a day of action on May 23, when the Costa Rican president visits Germany.
"We're asking for people all over Germany to let the minister of justice know that captain Paul Watson must be released immediately," society spokesman Peter Hammarstedt says in a video posted on the group's website.