Paul Watson, the prominent anti-whaling activist, was released from custody in Greenland five months after being detained on an international arrest warrant, his lawyer said.

Mr. Watson is the founder of a marine conservation group, Sea Shepherd, which has been known to aggressively confront whaling ships. He was arrested in July in Greenland, an autonomous territory of Denmark, and faced charges in Japan, one of the world’s most active whaling countries. But Danish officials decided to reject Japan’s extradition request, his lawyer said.

“I can confirm that Paul Watson has been released,” his lawyer, Julie Stage, said in an email on Tuesday.

“He is obviously relieved and is now looking forward to reuniting with his wife and children,” she added. “It has been five long months.”

The arrest had been based on a warrant issued by Japan in 2012 that accused Mr. Watson of interfering with a whaling ship and causing injury to one of its crew members in 2010.

In a video posted by a social media account for the Captain Paul Watson Foundation, Mr. Watson says in a windy, outdoor setting: “After five months, it’s good to be out, and good to see that they’re not going to send me to Japan. So now I go home for Christmas.”

Watson founded Sea Shepherd in 1977 after leaving Greenpeace, an environmental organization. Sea Shepherd is known for leading seafaring campaigns that directly interrupt whale hunting, shark finning and other contested maritime practices.

“My arrest has focused international attention on Japan’s continuing illegal whaling operations and their intent to go back to the Southern Ocean,” Mr. Watson, 74, told Agence France-Presse after his release. “So, in fact, these five months have been an extension of the campaign.”

Denmark does not have an extradition agreement with Japan. Peter Hummelgaard, Denmark’s minister of justice, said in a statement that since Mr. Watson had already been held for five months, the ministry wanted to ensure that period of time would be deducted from a potential sentence in Japan. He said the department, after discussing the matter with the Japanese authorities, could not be certain that would be the case.

The department also cited the length of time that had passed since the accusations against Mr. Watson.

Mr. Trump would be 82 on Election Day in 2028, older than President Biden is now. This year’s election is already his third consecutive time being the Republican nominee, after he won in 2016 and lost in 2020. In the modern party system, only Franklin Delano Roosevelt has ever received a major party’s nomination four times, though a handful have matched Mr. Trump with three.

“I am glad that the minister decided not to give in to Japan,” Ms. Stage, his lawyer, said. “As I have stated previously, I believe that the accusations against Paul Watson are groundless.”

Mr. Watson was the protagonist of “Whale Warsmega swerte,” a documentary series that aired on Animal Planet from 2008 to 2015 and followed his crew as it tried to stop whaling activities.