Hara was born in Hiroshima in 1905. Hara was a survivor of the atomic bombing of Hiroshima. While he was a middle school student, Hara became familiar with Russian literature, and also began to write poetry. He particularly admired the poets Saisei Murou and Paul Verlaine. He graduated from the English literature department of Keio University, and worked at a professional author from 1935 onwards.

Hara's wife Sadae fell ill in 1939, and died in 1944. He had once said of her, "If I should lose my wife, I would live only one year to leave a collection of sad and beautiful poems behind". A year later, just before the first anniversary of her death, he was exposed to the atomic bombing of Hiroshima at his parents' home in Motomachi. These two traumatic experiences became central to his work.

Natsu no Hana (Summer Flowers), his best-known work, for which he was awarded the first Takitaro Minakami Prize, was completed by August 1946 but not published until June 1947. Two further sections of the work were later published: “From the Ruins” (“Haikyou kara”) in 1947, and “Prelude to Annihilation” (“Kaimetsu no joukyoku”) in 1949. In works such as Summer Flowers and Chinkonka (Requiem, 1949), Hara describes and relates his terrifying experience of the atomic bombing. He also produced many poems on the same theme, for which he is perhaps better known in Japan.

Hara's final work, Shingan no kuni (The Land of the Heart's Desire, 1951) could be read as being his suicide note. He committed suicide in Tokyo on March 13, 1951, by throwing himself in front of an oncoming train. His already fragile mental state had been exacerbated by the outbreak of the Korean War, which seemed to confirm his ongoing presentiment of a dark future in history.

An epitaph to Tamiki Hara was originally built by his friends at the site of Hiroshima Castle. But it became a target for people to throw stones at, the ceramic plate on its front damaged and the copper plate on the back ripped off. So it was remodeled and moved to the present site next to the Atomic Bomb Dome.

On the monument is inscribed the poem in his last piece of writing, which reads:

Engraved in stone long ago,

Lost in the shifting sand,

In the midst of a crumbling world,

The vision of one flower.

The anniversary of Tamiki Hara's death was named Kagenki. A society of the same name was founded in September, 2000, by those who love his literary works. The society hosted an exhibition of materials concerning him to commemorate the 50th anniversary of Hara's death in 2001, and has a memorial service in front of his monument every year.