Born on March 1, 1892, the eldest son of the milk-producing merchant Niihara Toshizo in Kyobashi Ward (today Akashi-cho, Chuo Ward), Tokyo. Seven months after his birth his mother Fuku fell mentally ill, and he was taken in by the Akutagawa family (the adoptive family of her elder brother Michiaki). In 1904, at 11, he was formally adopted by the Akutagawa family. After Prefectural Third Middle School and the First Higher School, in 1913 he entered the English Literature Department of the College of Letters, Tokyo Imperial University. In 1914 he joined the third 'Shinshicho.' In 1915 he published 'Rashomon' (the starting point of his dynastic stories), and in 1916 'The Nose.' Praised to the skies by Natsume Soseki, he became at a stroke a new star of the literary world. That same year he graduated from Tokyo Imperial University and took up a post as English instructor at the Naval Engineering School in Yokosuka; in 1917 he published his first collection, 'Rashomon.' In 1918 he became an affiliate of the Osaka Mainichi Shimbun and devoted himself to writing, and the same year he married Tsukamoto Fumi. He published 'Tangerines' and 'Hell Screen' (1919), 'In a Grove' (1922), 'The Spider's Thread' (1924), 'Kappa,' 'Spinning Gears,' and 'A Fool's Life' (1927), one masterpiece after another, standing at the pinnacle of Taisho literature. As an intellectual writer combining academic record, education, and command of English, he was also at the center of literary discussion, as in the 'Plotless Novel Debate' with Tanizaki Jun'ichiro (1927). Yet in his later years he suffered from neurasthenia, stomach trouble, and insomnia, and early on July 24, 1927, in his study at home in Tabata, he took a lethal dose of sleeping pills (Veronal and Jalal), with a Bible by his pillow, and killed himself at 35. In his suicide note 'Memorandum Sent to an Old Friend,' he gave as the reason for his death 'a vague anxiety.' The suicide became a major event in the history of Japanese literature, symbolizing the end of the Taisho period.

A man of sharp sensitivity and thoroughgoing intellect. A man of exceptional culture versed in the classics, classical Chinese, and English literature, in completeness of technique he stood out above his peers in the Taisho period. Across a wide range of genres — 'dynastic tales,' 'Christian tales,' 'Meiji opening tales,' and 'modern tales' — he drew out a unique aesthetic and emptiness. On the other hand, nerves too delicate and perfectionism brought on his mental collapse in his later years. The existential suffering he recorded in his suicide note — 'Before me there is no light' and 'only a vague anxiety' — was handed down to later generations as the archetypal mental landscape of the modern Japanese intellectual. In looks he was famous for his black-rimmed glasses, slim build, and eyes tinged with melancholy.

Akutagawa Ryunosuke is positioned at the core of Japanese literature today as a representative writer of the Taisho period. In 1935 his friend Kikuchi Kan (founder of Bungei Shunju) established the 'Akutagawa Ryunosuke Prize' (Akutagawa Prize) bearing Akutagawa's name, which continues to this day as the foremost new-writer prize in the Japanese literary world and has produced Inoue Yasushi, Matsumoto Seicho, Oe Kenzaburo, Murakami Ryu, Murakami Haruki (nominee), Matayoshi Naoki, and others. The representative work 'Rashomon' was made into a film by Kurosawa Akira (1950, Venice Golden Lion, U.S. Academy Honorary Award), establishing the world standing of Japanese cinema. 'Yabu no naka' ('In a Grove'), the source of the idiom 'in the thicket,' is used internationally as the symbolic phrase for 'the relativity of truth.' In subculture works of the 2020s such as 'Bungo Stray Dogs,' he has also become a popular character. The site of his former residence in Tabata, Kita Ward, Tokyo, is open as the 'Tabata Literati Village Memorial Hall,' and Tabata is now a tourist district symbolic of the 'literati village.' On July 24, 'Kappa-ki' (memorial day), every year fans visit his grave and events mourning Akutagawa literature continue.