Steve Sawyer, a former executive director of Greenpeace International who narrowly avoided injury in 1985 when the environmental group’s ship Rainbow Warrior was sunk by sabotage in New Zealand, died July 31 at a hospital in Amsterdam. He was 63.

The cause was lung cancer, Greenpeace said in a statement. The American-born Mr. Sawyer was an Amsterdam resident.

While growing up in New England, Mr. Sawyer became a skilled sailor. He used his expertise to help to refurbish an aging British trawler for Greenpeace in the late 1970s and early 1980s.

Re-christened the Rainbow Warrior, it became the flagship in Greenpeace’s efforts to prevent nuclear testing and to promote ecology.

Since the organization’s founding in 1971, Greenpeace had cultivated a daring, anti-authoritarian and sometimes confrontational approach to environmental protection. Its members were sometimes called eco-warriors, even though nonviolence was one of the guiding principles of Greenpeace.

“For us, it wasn’t blind idealism,” Mr. Sawyer told the Toronto Star in 2005. “It’s hard to tell people who weren’t around then about living in daily fear of crazy old men in Moscow and Washington who had their fingers on the nuclear buttons, and might at any time cause the Big Bang.”

At different times, Greenpeace activists darted through dangerous waters in small boats to prevent Japanese and Russian whalers from discharging their harpoons. They landed on the coast of Siberia to protest Soviet whaling practices. They handcuffed themselves to drums filled with toxic waste to keep them from being dumped in the ocean. They protected baby seals about to killed in Canada, sometimes spraying them with green dye to make their white fur worthless to hunters.

Many of these guerrilla-like episodes were caught on film, adding to Greenpeace’s reputation as the renegade pirate outfit of the environmental movement. “Back then,” Mr. Sawyer told the Star, “one of the major requirements was that people who signed up didn’t mind if others thought they were nuts.”

In 1985, Mr. Sawyer was one of about a dozen Greenpeace crew members aboard the Rainbow Warrior when it embarked on a dual mission in the Pacific. The first was to remove inhabitants from the atoll of Rongelap in the Marshall Islands, which had been the site of U.S. nuclear tests in the 1950s.

Residents had unusually high rates of cancer and birth defects, but U.S. officials ignored their requests to move off the nuclear-contaminated atoll. Over a 10-day period, Mr. Sawyer and the Rainbow Warrior crew evacuated about 300 residents, their livestock and possessions to another atoll about 100 miles away.

The second mission of the Greenpeace crew aboard the Rainbow Warrior was to lead a flotilla to an atoll in French Polynesia, in an effort to block underground nuclear tests by the French. The Rainbow Warrior was docked in Auckland, New Zealand, when two bombs exploded below the ship’s waterline just before midnight on July 10, 1985.

The Rainbow Warrior was damaged beyond repair and listed to one side, half-submerged in the harbor. After the first explosion, Greenpeace photographer Fernando Pereira sought to retrieve his camera equipment. He was killed in the second blast.

There may have been greater loss of life if most of the crew members hadn’t been ashore, celebrating Mr. Sawyer’s 29th birthday.

New Zealand police quickly arrested a man and a woman who claimed to be Swiss citizens on vacation. Further detective work revealed that they were French undercover agents who had planted the bombs on the side of the ship, then fled with the help of accomplices.

After an international outcry, the two intelligence agents who planted the bombs were sentenced to prison, and a coverup scandal tainted the French government. With the legal help of onetime White House counsel Lloyd Cutler, Greenpeace sued the French government and ultimately received a settlement of about $8 million.

“I was generally sympathetic to Greenpeace’s environmental goals,” Cutler told The Washington Post in 1989, “and as I started working with them, I came to admire them tremendously.”

In 1986, Mr. Sawyer became Greenpeace’s U.S. director, overseeing a rapid surge in membership, donations and global recognition. Two years later, he became the executive director of Greenpeace International, moving to London and later to Amsterdam, where the group maintains its global headquarters.

Over time, Mr. Sawyer redirected Greenpeace’s focus toward efforts to fight climate change and develop sources of renewable energy.

“The environment has to rise to the No. 1 issue on the world agenda,” he told the Los Angeles Times in 1989. “The dramatic actions we were once known for aren’t always necessary these days to bring things to people’s attention. Sometimes we can just point a finger and it’s enough.”

Yet, in many ways, he and his organization were defined by the bombing of the Rainbow Warrior and their defiance in the face of what they called state-sponsored terrorism.

“It was my 29th birthday,” Mr. Sawyer said in 2005. “That’s something I can never forget. Every year I’m forced to remember it.”

Stephen Gregory Sawyer was born July 10, 1956, in Boston and grew up in Antrim, N.H. His father was an engineer, his mother a piano teacher.

Mr. Sawyer graduated in 1978 from Haverford College in Pennsylvania with a bachelor’s degree in philosophy. While contemplating his career options, he met a door-to-door canvasser for Greenpeace and soon joined the group. He raised money and did other jobs for Greenpeace, including leading the refitting of the Rainbow Warrior, which was converted to a sailing vessel.

He stepped down from day-to-day leadership of Greenpeace in 1993 but remained closely allied with the organization, participating in reunions of the Rainbow Warrior crew. He later helped found the Global Wind Energy Council, which he led from 2007 to 2017. He traveled throughout the world to help establish wind energy companies.

In 1988, he married Kelly Rigg. In addition to his wife, survivors include two children; a sister; and a brother.

After the sinking of the Rainbow Warrior in 1985, Greenpeace converted another ship and named it Rainbow Warrior II. (A new custom-built Rainbow Warrior III was dedicated in 2011.)

In 1995, the second Rainbow Warrior sailed to the French Polynesian atoll of Moruroa to lead a protest against nuclear testing. When French military commandos boarded the ship, attempting to arrest the Greenpeace activists, the crew members invoked the memory of the photographer who had been killed 10 years earlier.

When asked for their identities, they all gave the same name: Fernando Pereira.