On the morning of Aug. 6, 1945, Setsuko Thurlow, then just 13, reported for her first full day of duty in Japan’s increasingly desperate war effort. Together with 30 other girls, she had been recruited to assist with code breaking at a military office in Hiroshima.

The major in charge of the unit was exhorting the teenagers to demonstrate their patriotism when, at 8:15 a.m., a blast detonated over the city. Out the window, Ms. Thurlow saw a burst of bluish white light.

She was then thrown into the air, losing consciousness. When she came to, it was dark and silent, and she was pinned under parts of the wooden building.

“I’m going to die here,” she thought to herself.

More than 150,000 people are thought to have perished in the atomic bombing of Hiroshima 75 years ago this month. Ms. Thurlow survived, but the attack would shape the rest of a life spent fighting for the abolition of nuclear weapons — work for which she jointly accepted a Nobel Peace Prize in 2017.

Less than a decade after the Hiroshima attack, Ms. Thurlow arrived in Virginia from Japan to study sociology. Local reporters asked what she thought of an American hydrogen bomb test in the Pacific that year that had killed a Japanese fisherman.

Ms. Thurlow — then named Nakamura — did not hesitate. “I feel angry,” she said.

It was 1954, nine years after the leveling of Hiroshima, followed by Nagasaki’s destruction three days later. Many survivors were reluctant to share their stories, much less say anything that could be construed as criticism of the United States, which had occupied Japan after the war.

But Ms. Thurlow described how she had jumped over dead bodies to cross the city on that horrific day. “It was hell on earth,” she told the reporters.

Since then, Ms. Thurlow, now 88, has insistently told her story in unflinching detail to thousands of people at protests, conferences, schools and even on cruise ships. Three years ago, she delivered an acceptance lecture in Oslo when the International Campaign to Abolish Nuclear Weapons, or ICAN, won the Nobel Peace Prize.

Speaking on a video call from her home in Toronto last month, Ms. Thurlow said that “I am one of those who can tell a firsthand story of human suffering that the bomb caused. To me that was a very important moral imperative.”

She shares her memories not only to bear witness to what it is like to survive a nuclear bomb, but also to put political pressure on governments to get rid of atomic weaponry for good.