The recorded death tolls are estimates, but it is thought that about 140,000 of Hiroshima's 350,000 population were killed in the blast, and that at least 74,000 people died in Nagasaki.
The bombings brought about an abrupt end to the war in Asia, with Japan surrendering to the Allies on 14 August 1945.
But critics have said that Japan had already been on the brink of surrender.
Those who survived the bombings are known as hibakusha. Survivors faced a horrifying aftermath in the cities, including radiation poisoning and psychological trauma.
British photo-journalist Lee Karen Stow specialises in telling the stories of women who have witnessed remarkable events in history.
Stow photographed and interviewed three women who have vivid memories of the bombings 75 years ago.
This article contains details some people may find upsetting.
Teruko was 15 years old when she survived the atomic bomb in Hiroshima on 6 August 1945.
At the time of the bombing, Teruko was in her second year of nursing school at the Hiroshima Red Cross Hospital.
After the bomb hit, the students' dormitory of the hospital caught fire. Teruko helped to fight the flames, but many of her fellow students died in the blaze.
Her only memories of the week after the bomb are of working day and night to treat victims with horrific injuries, while she and others had no food and little water.
After graduating, Teruko continued to work at the hospital, where she assisted with operations involving skin grafts.
Skin was taken from a patient's thigh and grafted on to an area that had developed a keloid scar as a result of burns.
She later married Tatsuyuki, another survivor of the atomic bomb.
When Teruko became pregnant with their first child, she was worried about whether the baby would be born healthy and if it would survive.
Her daughter Tomoko was born and thrived, giving Teruko courage in raising her family.